June 192JJ WHITTAKER-“FASTNEBS IN TEXTILES” 165

more stable and no evidence has been obtained of their breaking down in the solutions studied.

It is also possible to calculate, on certain assumptions, the amount of sodium included in the ion complex. This calculation shows that in the higher concentrations dealt with (O-6y0) about one-quarter of the sodium is bound in the case of the “4B” and “meta” dyes, whilst with Bordeaux extra, it appears that only a very small fraction (if any) is bound.

SUBmARY The work here discussed shows firstly the

great importance of purity in any such investi- gation, and secondly the extreme difficulty of - obtaining even qualitative results for the par- ticle size of dyes when this (as is usual with electrolyte-free dye solutions) is below the limit for visibility in the ultra-microscope, Diffusion coefficients cannot, except in the limiting case mentioned, even give results which are of qualitative significance in obtaining the particle size, and it is doubtful if ultra-filtration measure- ments are useful.

In the investigation of the solutions of the two Benzopurpurines, it has been possible, however, to show that in 0.5% solutions, they both contain anion aggregates, which do not differ greatly in size, consisting of a few anions and perhaps 20 or 25% of the sodium. On dilution, however, the tendency of the micelle to break down is much greater with the “meta” dye than with the “4B” dye. This may be associated with some marked difference in the structure of the micelle, which in turn may be conneoted with, or have the same origin as, the difference in dyeing properties. Finally, Bordeaux extra has been shown to be a dye more nearly in true solution, with aggregates containing fewer anions and very little sodium. Sir William Ramsay Laboratories of Inorganic

and Physical Chemistry, and Imperial Chemical Industries Ltd.

LONDON SECTION Joint meeting with the London Section of the

Textile Institute held at the Barrett Street Trade School, on 8th February 1934, Mr. F. W. WALKER in the chair.

Fastnmi in Textiles C. M. WHITTAKER, B.Sc.

It should be clearly understood that this paper is to be regarded solely as the work of a private individual. The author’s colleagues on the Fastness Committee of the Society of Dyers and Colourists are not associated with anything it may contain, and it must be emphasised that he is not dealing with the subject in his official capacity as a member of Messrs. Courtaulds’ staff.

The paper is intended deliberately to be provocative so as to givti others an opportunity of stating their opinions.

The popular national Press has had much to say lately about a new elastic yarn and, as usual, absurd claims about its potential revolutionary effect in the trade have been put forward. After 33 years’ experience in the textile trade, how- ever, the present author &es fully that revolutions in textiles are not made in a day. On the c o n t r q , it is doubtful if any single idea relating to textiles has ever met with Iarge-scale success, except after a long period of development work.

The chief property of the new yarn is its elasticity, but it would appear that the present subject, “Fastness in Textiles”, is more “elastic” in its general implications than all textiles put together. All those who have any dealings with fibrous materials are aware of the many different views regarding fastness of dyes, and the extraordinary difficulties whioh dyers frequently experience in getting specifications of the degree of fastness required. Moreover, the enormous variety and uses of textiles have re- sulted inevitably in the creation of widely varying standards offastness. It is obvious, e.g., that hangings for the interior of a cinema which wi l l never see the light of day, are not required to be as fast to light aa the hangings for a hotel at the seaside. It is obvious a h that a fine- gauge silk stocking need not be as fast to washing as a coloured table-010th.

The present author haa suggested from time to time during many years that the fuller the particulars of the fmtness requirements which are supplied to the dyers by customers, the more efficient and cheaper will be the service that dyers can give. Many fast dyes are wasted in fabrics which do not require them because of inadequate specification as regards fastness. On other fabrics, poor and unsuitable dyes are used, yet some firms think that dyers are probing into their innermost secrets if asked to give the type of fabric for which they require yarn of a certain shade. Much talk is heard nowadays of the necessity for co-operation, and it is indisputable that more co-operation between the dyer and the manufacturer would be of mutual advantage and lead to economy in production.

The kind of fastness with which it is intended to deal first is “Light Fastness”. The various interpretations of this property are responsiblc for many absurdities. Perhaps the major absurdity is the term “Guaranteed Fadeless”. Literally this meam a guarantee that the shade will never fade, although it has been suggested humorously that it means “fade less than other fabrics”. There is no room for quibbling over the literal meaning of the word “Fadeless”, but the lyricism of that modest profession whose motto is “Truth in Advertising” cannot resist the temptation to paint the lily, and so we may read that a range of coloured fabrics is

166 WHITTAKER-“FABTNESS IN TEXTILES” [Juros 1034

“Absolutely Fadeless”. Surely ((Fadeless”. if taken literally, does not require any qualifica- tion, such as “absolutely”. Qualifications of this kind are reminiscent of the abuse of super- lativeR in the language used in film advertise- ments.

Many people who can rcmcmber the first so- called fadeless fabrics which appeared in com- merce, are able to recall the fact that the range of colours was limited to very heavy dull shades, which were admittedly of outstanding fastness to light, but were not, of course, fadeless. They would probably last, however, as long as was required by the normal consumer. As taste and design changed, a demand sprang up for brighter colours and pastel shades, which also have been included in the so-called ‘(fadeless ranges”, with the result that the meaning of the term (‘Guaran- teed Fadeless” has suffered so much degradation that it has become merely a synonym for a vat- dyed fabric, and the distributors are compelled to limit their guarantee to so short a period a8 12 months in many cases. Yet so keen has com- petition become in the depression from which we all hope we are now emerging, that the term “Guaranteed Fadeless” need not now even mean vat-dyed.

Casement fabrics containing cotton, viscose rayon, and cellulose acetate rayon are now on the market, but it is quite obvious to any technolo- gist that a fabric containing these three fibres cannot be vat-dyed in the majority of instances. It is agreed that the cotton and viscose rayon may be vat-dyed, but it is also commonly agreed that the cellulose acetate dyes, over a commercial range of shades, are not as fast to light as vat dyes of “casement fastness” on cellulose. These fabrics are included, however, in fadeless ranges, so that the degradation of the term ‘ (Fadelem” proceeds apace.

It is customary in the dyehouse controlled by the author to analyse yarn-dyed fibres for the class of dye used, and it is amazing to find how large a number of faultily “constructed” fabrics from tho light-fastness point of view are on the market. Amongst these are a large number of casement and furnishing fabrics in which the cotton is dyed withvat dyes, and theviscoserayon with direct cotton dyes. The author suspects that one of the reasons for this is that many yarn dyers do not care to use vat dyes on viseoae rayon, but it is obvious that a fabric of the type mentioned is faultily “constructed”, because the direct cotton colour-dyed yarn will inevitably fade before the vat-dyed yarn; thus, it gives un- satisfactory service to the ultimate consumer.

A very fancy yarn-dyed casement cloth was examined recently and 11 distinct shades were found; 6 of these were vat dyes and 6 were direct cotton dyes. What is to be gained by the con- struction of such a fabric ‘1 The technical ;gnorance, which makes such a state of affairs possible, is to be deplored.

Most dyers and colourists are aware. that this Society, the German Fastness Commission, and the American Textile Chemists’ Association, have each spent much time and money on the establishment of standards of fastness to light. It is hoped to reach a common agreement eventually, so that it will be possible to adopt one set of international standards for fastness to light. Meanwhile, the English and German standards are wool patterns dyed under specitied standard conditions, in definite percentages with definite dyes. Wool has been chosen because it is the fibre on which dyes are the least sensitive to moisture and sulphur fumes, etc. in the atmosphere. It should be realised clearly that these standards are definite patterns and not dyerr . * The present author has protested more than once against the present abuse of these standards, in classifying the fastness to light of dyes. Since no known dye is equally fast to light in pale and heavy shades, it is obvious, of course, that no dye can be of one standard of fastness in all depths of shade. Therefore, it is impossible to classify a dye as equal to a particular standard, unless the actual yo of the particular dye, which is equal to the standard named, is stated. Yet we find dyes classifled on the pattern cards, e.g. as 8, the highest, standard, whilst the pattern card itself may contain four or five different percentages of this dye. Such a classification is inaccurate and cannot be justified. The present author suggerrts that the % of the dye, which is equal to the standard named, should be put on the pattern card itself; it is such a simple solution of the problem that it is surprising to find that it has not yet been adopted.

All dyes tested by the author are exposed in a range of eight shades. This enables a rapid and reasonable comparison of the relative fastnesses of the dyes to be made, by comparison of the relative fading of the eight depths of shade.

Sixty of the fastest-to-light commercial direct cotton dyes, e.g., were exposed last year in this way. Eight of those which wcre considered to be the fastest-to-light, were chosen to give a range of yellow, orange, brown, red, blue, green, and grey shades. These dyes were exposed next in four different depths of shade on viscose rayon, ahd cotton; the results were astonishing to all who aaw them. They confirmed the view that a dye on cotton is much less fast than a similar d e of the same depth of shade on viscose

does not appear to have been stated on any fastness-blight classification dealing with vis- oose rayon and cotton.

It was discovered also that there is no direct cotton blue, grey, or green which is equal in fastness to light to the best direct cotton yellows, oranges, and reds. This is an astonishing fact, but it is suggested that the light classification tables which are published at present, do not indicate this result. If, on the other hand, the author’s suggestion in connexion with means for

rayon. $ his fact was known, of course, but i t

W Hl’ l ’ ’ rA~iK)C- ‘ ‘~ ’A~rN~:~ 1N TEXTILES” 167 .IiI1K 1#64]

stopping the abusc of the use of these light fastness standards were adopted, the fact under discussion would emerge from the tables. The present position with regard to this pmticular example is a disturbing one, because it means that if the fastest-to-light direct cotton yellow, orange, brown, or red, is used, there is not a single direct cotton blue, grey, or green of equal fastness to light which may be used with them for “drabbing” purposes in compound shades. Therefore, it is impossible to produce a balanced fade in compound shades if these fastest dyes are wed. In other words, unbalanced fades in three colour mixings are obtained.

It is sometimes uuggested that the best direct cotton dyes are almost equal in fastness to light to the vat dyes. In the author’s opinion, this view is absurd. The direct cotton dyes cannot he compared for light fastness with the vat dyes.

((,bmpralioe mpo8ure tutS of mn1erk.l.s &led i i dh vat dye8 and with the fmtut-to-light direct cotton dyes were shmt. in order to demonstrate t h truth of this statement).

The next part of the subject with which it is proposed to deal, is that concerned with the liability of caaement curtains to tendering on exposure. For some years past, the distributors have had complaints about the tendering of curtains after being hung; in some instances, this defect has occurred in a relatively short time. Many of the curtains have contained rayon as well as cotton, and the rayon, being initially weaker than the cotton, has frequently given way first. Nevertheless a detailed examina- tion has shown that the cotton has deteriorated relatively as much as, and in some cases to a greater extent than, the rayon. These com- plaints are very annoying to all concerned, and many people, in ignorance, have put all the blame on the rayon, and have raised in many quarters an unjust prejudice against the use of rayon in casements. Experience gained during many years has shown that, these tendering complaints occurred in all tones of yellow and orange, occasionally in red, but never in blue. Obviously, if the rayon were at fault and not the dye, complaints should cover the wholg range of casement shades, but, fortunately, they do not. Scholefield and Landolt, amongst others, have made contributions towards a solution of the problem, but no generally accepted explana- tion has yet been put forward. A11 workers are agreed that certain vat dyes accelerate unduly the tendering of cellulosic fibres on exposure. Direct cotton dyes, as a class, do not cause this tendering. The prejudice against rayon in casements due to this experience became so marked that the present author and two of his colleagues, Delph and Hegan, have carried out joint work on this subject for over 3 years. This work was summarised in a pper given before the Manchester Section of the Society in November 1932 (this Jour., 1933, M, 9). The results showed clearly two points-

Certain vat dyes unduly accelerated the tendering of celluloaic fibres on exposure, and viscose rayon did not tender relatively a t a greater rate than cotton when dyed with these dangerous vat dyes; if dyed with the safe vat dyes, rayon was perfectly suitable for usc in casements.

In collabomtion with the Allied Trades Federation of Dyers, Bleachers, and Finishem, and all the dyestuff manufacturers, a Ibt of safe vat dyes for use in casement dyeing has now been circularised to the trade. Despite thene preca,utiomry steps, however, it is to be re- gretted that the dangerous vat dyes are still being used in some instances for ca.sements. Un- fortunately, some of them are amongst the cheapest of this class of dyes, and the pricc- cutting, which still obtains in the dyeing of vat shades, explains, no doubt, the short-sighted policy involved by the continued use of tlivsc dyes.

Whilst on this topic, it may be of interest to give one or two of the results of our work on thc tendering question during the summer of 1933. It has always been puzzling to. determine why the complaints arise in so haphazard a way; e.g., many sets of curfains will be made out of the same batch of dyed yarn, yet only one set of curtains out of this batch is the subject of a complaint. If one set becomestender, why do not they all become tender Z The explanation, of course, is that the local conditions under which the curtains me hung vary widely. The question arises as to what are the variable factors ? Our work h t summer has illustrated one of them, viz. that the rate of flow of air over or through the curtain is of outstanding importance. This was proved in several ways; e.g., pieces of the same fabric of viswe rayon were pinned on to a board-and on to a frame. More air obviously F e d through the fabric on the h m e . Dupli- cate seta wen4 exposed: one on a roof 42 ft. above ground level in a very exposed position, and the other on a roof 24 ft. above ground level and much more eheltered. The exposure period was from the loth to the 24th May 1933, when 38 sun-hrs. were recorded. The fluidity tests on these fabrios were as follows-

Iiicreasc In Fluidity Fabric ou frame at 42 It. 11.4 w i t s

,, board at 42 it. 4.6 ,, ,, . frameat 24 it. 6.7 .I

,, board at 24 ft. 3.8 ,,

A frame was made next on the weather vane principle, so that the patterns on it were always facing every breeze that blew. The following fluidity figures, in an exposure from 16th to 23rd June 1933 were obtained; 23 sun-hrs. were recorded during the period- $

YHW Fixrd U w i l Fraiiic

160127 Viscosc! rayon ... 8.4 7.5 3.3 1/36 Blcached Egyptlaii cotto;;’ 10.1 120 10.6

Delph has shown that this increase in degrada- tion is due to the mechanical displacement of the threads by the increased flow of air, with the

168 WHIYl’A KER-“FASTNE SS IN TEXT1 L E S” [.lui!s 19JJ

result that more surface is available to be de- graded by the light and atmosphere. It is obvious, of course, that there could be no short- age of oxygen, even on the board, but that the result was due to the extra surface exposed to chemical attack as a result of the mechanical displacement. This view is confirmed by the fact that a range of undyed viscose rayon yarns from the finest to the coarsest denier (78/18 to 500/64 denier) was exposed, and it was found that the finest denier tendered the most rapidly under identical conditions of exposure. The 76/18 denier yarn showed an increase in fluidity of 4.4 units in 20 sun-hrs. from 27th June to 3rd July 1933, and 11 units from 6th July to 17th July 1933 in 62.8 sun-hrs., whereas the 600/54 denier yarn only increased 0.7 and 6 units respectively in the same periods.

The yarns of intermediate denier fell between these two extremes with almost mathematical accuracy. The above results show that the lowest denier (finest) yarns deteriorate to a greater extent than the higher denier (cowm) yarns. This result was anticipated, as the fine yarns have a greater surface per weight of yarn oxposed than have the coarser yarns. If t h o main attack on the yarns is on the surface, a greater percentage of the fine yarns will be attacked than of the coaraer yams. These re- sults, therefore, show that the most suitable viscose rayon yarns for casement fabrics are the coarse yms. It is clear also that the construc- tion of a fabric plays a very important part, and that a leno weave must tender more rapidly than a repp. The work thus explains one fact in this perplexing problem. It would be of interest if the conditions under which each set of ten- dered curtains were used, were known accu- rately, but this is impossible. It can be anticipated, however, that a curtain hupg near a window which is frequently left open, is much more likely to tender than a curtain placed in a relatively stationary position, such as a large window on a staircase.

Fa8tne88 to Wmhing-This is not a fastness property in textiles which is difficult to achieve, nor does it lead to much trouble in these days. Provided the manufacturer is prepared to pay a reasonable price for the shades required, the dyer has at his disposal a large range of vat, azoic, and sulphur dyes, in order to produce faat-to-washing articles. There is no technical diiliculty in pro- ducing a complete range of shades which will withstand the severest washing, except in the brightest emerald, purple, and pink shades usually obtained with basic dyes.

The Fastness Committee of the Society of dyers and Colouriats has a Wishing Report in preparation for publication; it includes a range of washing standards, and a standard method of testing.

The misuse of the so-called “oxygen washing powders” has ctlused trouble from time to time. These powders are liable to exert a severe

stripping action on sulphur dyes and, in the author’s opinion, this type of dye should not be used in the highest class of washing articles. Difficuities arise, of course, in the fastness to washing of certain classes of goods, especially when the dyer is limited in price, because he is compelled often to use dyes which would not be included in a really satisfactory range.

One frequent source of complaint about looseness to washing is due to the use of unsatisfactorily dyed trimming, which is not intended by the actual manufacturer to be fast to washing. It often happens that con- trasting-colour cuffs and collars of a non- washing material are used on a garment, the main portion of which is made from a fast-to- washing dyed material. Nowadays, it is quite common to find that the cheapest shirts sold in chain stores have been dyed or printed with vat or azoic dyes. It follows, therefore, that if cheap lines of this kind are dyed with these fast-to- washing dyes, the higher-priced articles must also be dyed with a similar class of dyes.

Competition in the soap trade also has led the big firms to operate Washability Bureaux and Demonstration Hihops. At these places, a CUB- tomer can havc a piece of material washed and an opinion given before actually purchasing the material.

Fastness to Shrinking-This is a problem which has received a great amount of attention with very satisfactory results. Shrinkage has led to bitter complaints from the distributors of case- ments, underclothing, shirtings, and overalls. It has to be admitted that the craze for cheapness is responsible for some of these unsatisfactory fabrics, because the finisher has been compelled frequently to deliver cloths of a definite length and width or to lose the business. In order to obtain this length and width, cloth has, on occtlsions, to be stretched considerably, with the result that the first time it is wetted it recovers it.s natural length. On the other hand, with the best will in the world and taking every available pre- caution to prevent stretching, fabrics are inevi- tably stretched slightly in weaving, dyeing, and Whing. As regards the shrinkage of casement curtains, it should be realised that when viscose rayon becomes damp or wet it lengthens to a maximum of 6%. If the casement curtain, therefore, is cut whilst the fabric is damp, it will inevitably shrink when it reaches a warmer atmosphere. It is the practice of the present author to advise makers-up of curtains to cut slightly more than the length they require, and to hang the cut lengths in a dry room before they proceed to make the hems. If this procedure is adopted, it will be found that complaints about curtains runningup will be lessened materially.

Recently it has been announced by the Wool Industries Research Associtition that they have evolved a process for making wool unshrinkable. As regards cotton material, two analogous pro- cesses have been patented almost simultaneously

. / N W 1934 I W H I T A KE IC--"PI UMHN'I'S AN0 LAKB COLOURS AN L, THElH. APPLICATIONS" 160

in the United States and England. The chief claim made for these processes is that fabrics which have been submitted to them can be guaranteed unshrbikable. It should be remem- bered, however, that the cloth has been reduced in length and width during treatment, so that there is more yarn in a yard of unshrinkable fabric than in a yard of the fabric prior to shrinking. Thcrefore, oonsumers must be pre- pared to pay a little extra for this improved material. It is to be hoped that the public will be sufficiently long-sighted to support the efforts of the finishing trades to give them still more sat- isfactory articles. It is also to be hoped that the merchants will allow the finishing trades to reap some pecumary benefit from their research work.

Whilst not really a question of fastness, a few final remarks may be made on the matter of uhade in corsets. Part of the present author's work is, perhaps unfortunately, to dye yams for corset cloth, vorset webbing, and corset trimming manufacturers. Each in turn has criticised the matching of the shades, and ell, with one accord, have said that the fabric, the webbing, and the trimming must be exactly alike in tone, whilst their attitude in connexion with the rejection of deliveries, etc. often savours of tyranny. It would appear that, after all, the ultimate wearer of the corset is relatively inmerent to the exaot tone, and the reason for this insistence on it by the manufacturers is di5cult to trace. It is to be noted that this inuistence increases in in- verse ratio to the rate at which the particular line of goods is selling. It has been stated from time to time that the final customer will not have

blue-tone pink; but if the daily press were to publish a statement to the effect that famous film stars were wearing blue-pink lingerie, the dyers would be blamed quickly if they delivered a tea-rose pink shade.

It was only when Britain went off the Gold Standard, and adopted a protective policy, that certain people were attracted to the corset trade, and an interesting fact emerged during the ex- amination of a large number of foreign-made corset cloths, viz. many of them were dyed with pink basic dyes; consequently, they were ex- tremely f@tive. Probably this practice is a relic of the days when real silk, dyed with Eosin or Rhodamine, was used in making corsets. No English d er could imitate these shades without

complaint of fading was received, the dyer waa condemned as incompetent in comparison with his Continental confrire. When, however, the fastness of samples of the Continental fabric was determined in a comparative manner with dyeings made by the author, it was found that exposure for 3 days in February was enough to show the fugitive nature of the Continental fabric, but when the exposure tests were shown to the merchant concerned, he would not believe the evidence. Truly, the lot of an honest dyer is hard !

the use o fy the same basic dyes. Immediately the

SCOTIlsH SECTlON Meeting held at the George Hotel, Buchanan

Street, Glasgow, on 22nd December 1933, Mr. JAMES BRUOE in the chair. Pigments and Lake Colours and their Applications

A. H. WHITAKER It iN intended to deal only with the morc

important pigment and lake colours. During post-War years, the range of them

products has been augmented uo considerably that many of the older pigments have suffered considerable eclipse. Prussian Blue and Vermilion were prepared

first in this country over 100 years ago, and the recipes for their manufacture remained secret and more or less unaltered until post-War years. Even within the last quarter of a century, employees at some colour works are believed to have been told to adhere rigidly to such instruc- tions as stirring the contents of a vat or vessel for so many minutes clockwise and so many minutes . anti-clockwise, in order to obtain the best possible resulte.

Pruseian Blw-These can be sub-divided into Potash Blue and Soda Blue; the terms Milori and Chinese Blues are applicable only to types of these, although such names are still used generally:

Genuine Potash Prussian Blue is the most im- portant of all; it is formed indirectly, e.g. by precipitation of ferrous salts with potassium ferrocyanide and oxidation of the precipitate with suitable agents, e.g. sulphuric and nitric acids, ferric sulphate, pohssium bichromate and sulphuric acid, hydrogen peroxide, and also by oxidation with air alone. Blues made by using different oxidising agents, differ sllghtly in strength, texture, shade, and in bronzing or non- bronzing properties. At the same time, dilution, coupled with the "striking" tempera- ture, have a very marked bearing on all these properties. During post-War years, very satis- factory non-bronzing blues have been evolved; they are eminently adapted for use in the manu- facture both of paint and cellulose lacquers. They have not the clean and green undertone that the bronze Potash Blues possess. The chief uses for Prussian Blue are in the manufacture of paint, printing ink, carbon papers, typewriter ribbons, and linoleum, whilst the cheaper types, e.g. pulp Soda Blue, are used in staining paper. The colouring matter in the blue paper sugar bags, a t one time consisted of Soda Blue. Prussian Blue is sensitive to minute traces of alkali, but owing to the fact that it is a com- paratively cheap pigment, its us0 in the near future is not likely to diminish to any serious extent.

Vermiliwn-This is a polysulphide of mercury and is an expensive pigment. The shades of genuine English Vermilion vary fiom a very pale shade of ormge to a scarlet. The manu- facture of Vermilion. in this country is in the

170 M“l’AKEll--“PIQMENTS AND LAKE COLOUICS AND THEIR APPLICATIONS’’ [Jw 6 1934

hands of only a few, and the secrets controlling its production in bulk have been guarded jealously for years, although it is considered that the mah point to be observed is efficient agitation of the heavy reacting mixture.

17ltramarine Blue-The term “Ultramarine” wa8 originally used for a deep blue pigment obtained in the early middle ages by a very complicated process from Lapis Lazuli, a semi- precious stone that is still greatly appreciated. Commercially, Ultramarine Blue is formed when a mixture of sodium sulphide, alumina, and ijilica in suitable proportions is Wlcined. The raw materials uned are china clay, anhydrous sodium carbonate, Glauber’s mlt, sulphur, carbon, and a certain proportion of silica. The colour of Ultramarine Blue haa never been successfully imitated with an organic colour or colours. Although its staining power i8 poor, it hatl H, very rich-loom appearance when applied with the necessary media, and also

, possesses excellent fastness to light. It is sensitive, however, to acid, but is used in practically every traclc where a blue pigment is required. It is used in paints and cellulose lacquers extentively ; also in the rubber, printing ink, and paper coating trades, in the manu- facture of artists’ colours, and in poster,work. . Zinc Oxide or Zinc White and Lithwpme- The name “Orr”, in this country, is associated very intimately with both these pigments, since much of the early pioneering work in this field was done by the Orr family at their works in Lancashire. Zinc oxide is made by heating either the metal itself or its ores in the presence of air. Many tons of this material axe used annually in the manufacture of paint and distempers,

Lithopone is a mixture of barium sulphate and zinc sulphide. When it was introduced, it was claimed that it would replace White Lead entirely, particularly as it is much less poisonous, but it has scarcely fulfilled the original expecta- tion in this respect,although its use appears to be extending steadily year by: year. Besides its use as a pigment for the paint trade, it is used in very large quantities in the rubber industry.

White Leud-This pigment is a baeic lead carbonnte and is more extensively used in the paint trade than any other white pigment. It possesses exceptional covering power, but is very poisonous. Efforts have been made in recent years to supplant it either partidly or entirely, and the chief progress that has been made in this direction has been in the manufacture of Titanium White and other titanium compcunds. Unless the prim of titanium oxide is reduced considerably, however, there is not much possibility of it supersedhg White Lead.

The covering power’ of Titanium White appears to be excellent. Moreover, when mixed with coloured pigments, it yields products of good stability to light and weathering.

.

Baryta-This is a natural pigment occurring in various parts of England and Scotland; its price varies according to quality. Barytes is used mainly in the manufacture of paints.

Commercial Blanc Fixe is usually a by- product obtained in the manufacture of hydro- gen peroxide; it differs considerably in physical properties from a Blanc Fixe prepared, e.g., by precipitating a solution of a barium salt with aulphuric acid. The obliterative power .of Blanc Hxe prepared in the latter manner, is consider- ably greater than that obtained with the former, and when incorporated with a colour it gives a far better finish; hence, it is used largely in printing inks, whereas the former product is used chiefly in paints and pulp colours.

Alumina or Aluminiuwt Hydrozirle ajnd Alumina-Bhnc Fixe-These are used chiefly in printing ink colours. Different qualities of aluminium hydroxide can be prepared by m o w the temperatures and dilutions of the reacting salts. GeneraUy, an “alumina”, which has been “struck” at a low temperature, has far better finish than one “struck” at a high temperature. This base is used very extensively in the printing ink trade, but rarely in the paint trade, owing to the fact that it induces livering of the products. Alumina-Blanc Fixe is pre- pared by adding a solution of soda ash to one of aluminium sulphate and then adding sufficient barium chloride to precipitate the free sodium sulphate. It has been found also that in the manufacture of both Alumina and Alumina- Blanc Fixe, the finieh as well aa the settling properties are considerably improved by small additions of Turkey Red oil and/or other similar materials.

Satin White-This is a mixture of calcium sulphate and alumina, and usually is prepared by double decomposition of aluminium sul- phate and milk of lime. It is used in the paper trade chiefly as a coating agent and imparb a very h e 6nish to the material.

Fiinely-ground Silica-Various qualities of this me offered byseveral h s in the country; it is used as a bme in the preparation of paper- surfacing colours and also to some extent in paint. It has less opacity, however, than Blanc Fixe. A particularly good grade of silica is sold under the trade name of “Milowite”.

Qjpmm-This baae consists of hydrated calcium sulphate. Plaster of Paris is the name given to the e l y hydrated product; it is produced by heating the purer forms of gypsum st a temperature of about 190” C. This material has only very limited uses in the paint trade, but dead-burnt calcium sulphate is used to a very large extent in dry distempers.

China Clay--This material is generally used as base on whioh to “strike” colours in order to give greater bulking properties. It is particularly inert and can be used safely, there- fore, aa a baae without possibilities of inter- aation.

Juns 19341 WHITAKER-‘‘PIGMENTS AND LAKE COLOURS AND THIER APPLICATIONS” I 71

Creen Earth and White Earth-These sub- stances arc mined in various parts of the world, and vary largely in composition according to their sources; they are formed by the breaking up of complex silicates. White Earth is similar in constitution to Green Earth, but contains much less iron. These Earths possess the remarkable property of absorbing basic dyes and imparting much greater fastness properties to the resultant colour than would be the caae if the ordinary type of base, e.g. Blanc Fixe, were used on which to precipitate the dye.

A range of colours used very extensively before the War is of only minor interest now. It includes the following-

Cochinea-This is derived from the female cochineal insect. The bright red alum-tin lake prepared from Cochineal has been known for a long period. It is extremely fast to light, but the results of tests carried out by the present author indicate that it is by no means a per- manent colour. Moreover, it is very expensive and does not show good colour value. Lakes pre- pared from Helio Past Rubine 2BL (I.G.) are not onlycheaper and brighter, but verymuch faster to light. In spite of this, however, many Municipal Authorities insist that certain of their paints shall contain genuine Cochineal and no other colouring matter.

Persian Berries and Quercitron Bark-These yield the so-called Dutch Pinks, which still have their uses in the paint industry. They are precipitated either with alum or chalk.

Logwood Ln.kes-These are usually prepared by precipitating Logwood “Crystals” with tin or iron salts on a mixture of Alumina and Blanc Fixe. An intense, rich black lake is obtained, which, although lacking in staining power in comparison with Carbon Black, finds a great use in cellulose lacquers on account of its non-bleeding pro- perties.

R a e Pinks-These are prepared from Brazi- lian or Mexican Lima Wood by precipitation with sulphate of alumina on a Whiting base.

Vandyke Brown-This is a natural mineral product, mined in various parts of the world; it is deep brown in colour and is usually purified by extraction with hot dilute caustic soda.

Carbon Black-This is obtained in two ways- (1) By heating carbonaceous materials, e.g. wood, bones, etc., out of contact with air, or (2) by burning hydrocarbon oils and resinous materials in an insac ien t supply of air. The latter method gives Lamp Black.

Carbon Black probably is used in far larger quantities than any other black pigment. It is cheap, has good colour value, and has very important uses in the paint, rubber, printing ink, and paper surfacing industries.

Bone Black and Ivory Black-De-fatted ground bones are heated in iron crucibles in

absence of air. The best Ivory Blacks are very rich colours, but do not possess the colour strength of Carbon Black.

Yellow and Red Ochres-A class of pigment colours, which is used extensively in the paint trade and to a lesser extent in the printing ink, rubber, and paper surfacing trades, includes the naturally occurring compounds known commercially as Yellow and Red Ochres. The shades of these products depend on the content of ferric oxide and hydroxide. Yellow Ochres are mixtures of clay or calcium carbonate with ferric hydroxide, and Red Ochres contain in addition to these components, varying amounts of red ferric oxide.

Raw and Burnt iYienm-These are similar to the Ochres, both in composition and appearance, and are excavated from the earth in the form of dark brown and yellowish- brown pigments; they furnish a bright yellow to brownish-yellow powder on grinding. Siennas represent the purest native form of ferric hydroxide; they are greatly changed by calcination, forming the burnt Siennas of commerce. The calcination process changes both the form somewhat and also the colour, the latter becoming brown, reddkh-orange or red, according to the purity of the raw material. Ochres and Siennas have exceptional fastness to light and, in general, good covering power; consequently the purer forms, mixed with suitable media are still in great demand by artists. Several firms in this country and abroad are preparing iron oxides synthetically, and it is possible to obtain a wide range of shades of good brightness.

Perhaps the most important class of artificial inorganic colouring mattera are the Chrome Yellows.

Zinc Chrome-This has a very fine primrose- yellow shade, and is obtained by treating Zinc White in suspension in water with a calculated quantity of concentrated sulphuric acid and afterwards precipitating with a concentrated solution of potassium bichromate.

Lead Chroma-These are obtainable in shades ranging from a pale primrose to a deep orange. The method of manufacture varies, but it is generally accepted that it is most economical to start from basic lead acetate prepared from lead and acetic acid. Some makers still persist in using litharge, lead nitrate, and sugar of lead, but the cost of the finished Chrome is higher than that obtained by using lead as raw material. The shades are con- trolled, of course, by a number of factors, e.g. temperature, dilution, basicity of lead salt, presence or absence of free acid, or of free alkali. A small amount of aluminium sulphate is generally used with the paler shades of these pigments. Lead sulphate dso is used con- siderably to obtain paler shades.

179 WHITAKER-“PIGMENTS AND LAKE COLOURS AND THEIR AI’PLICATIONS” [June 1934

In the case of Orange Chromes, it is customary to work with very concentrated solutions and also to “strike” the Chrome at or near 100” C. Great care has to be taken in washing pale shades, since, after a few washes, the pigment becomes exfoliated in condition and settling becomes rather a diEcult matter. It has been found that certain agents, e.g. sodium sulphate, assist settling when washmg the Chrome, with- out detrimentally affecting the shade. Chromes are used largely in the paint and printing ink trades, but most of them, particularly the paler shades, are inclined to darken and sometimes to blacken on exposure to light. Various theoretical explanations of these changes have been propounded, but it is the author’s opinion that atmospheric con- ditions play the most important part. The temperature used in drying Chromes is also a very vital factor. The paler shades usually have to be dried at a comparatively low tem- perature, but the middle and orange shades can be dried at a fairly high temperature. Chromes are obtainable also as pourable pulps of 50 to 60% solids. This finely dispersed type is generally used in calico printing. The ordinary types of pulp Chromes, of varying strengths and shades, are used extensively in the paper coating trade. Most Chromes are sensitive to alkali, the paler shades becoming deeper. This behaviour precludes their extensive use in certain directions, and, coupled with the defect of darkening on ex- posure to light, has contributed to the introduc- tion of successful imitations with permanent organic colours on suitable bases. A guarantee can be given with such colours, whereas with a Chrome there is always doubt.

Chrome Greens and Brunawick areens-These consist of suitable mixtures of Lead Chrome and Prussian Blue. The purer Greens contain no substrate, whilst Reduced Greens contain Blanc Fixe, Barytes, Whiting, or any other suitable base, depending upon how the colours are to be applied. The methods of manufacture vary considerably. Many of the products show a distinct tendency to cause flotation of the blue when added to paint media, but this defect can be eliminated to a great extent by producing a soluble Prussian Blue and “striking” the Chrome on this. The method is by no means an easy one and accurate control of the desired shade is difficult, although if temperatures, dilutiona, rates of running-in, etc. are adhered to rigidly, it is possible to obtain fairly consistent results. Hundreds of tons of Brunswick Greens are used in this country annually; their chief use is for paints, although outlets are found in sundry other trades, e.g. the manufacture of crayons, pencils, rubber, cellulose enamels, end linoleum. It is impossible, of course, to give detailed information of the actual manu- facture of Chrome and Brunswick Greens, as nearly all manufacturers have their own special methods. Two things can be recommended-

(1) the addition of a small amount of tartaric acid at the end of “striking” the Green to help to preserve the shade; and (2) additions of soluble salts, e.g. barium chloride, which help to simplify the subsequent washing.

Perhaps the most important range of lake colours is that prepared from basic dyes. Repre- sentative dyes used are-Auramine, Methyl Violet, Rhodamine, Safranines, Rhodulines, Nile Blue, and Methylene Blue.

Eosin ale0 is usually included in this range. A concentrated lake of the dye is prepared by precipitation with lead acetate or nitrate. In pre-War days, Eosin lakes were used in very large quantities in this country on account of their exceptional brilliancy, par- ticularly in the printing ink industry, but owing to an increased demand for fast-to-light colours, their manufacture now is distinctly limited.

Helio Marine is the name given to the lake produced by precipitating Methylene Blue with an acid dye, e.g. Acid Alizarin Blue. Tannic acid, tannin, and tartar emetic, rosin soaps, Tamol NN, and Katanol are also used as precipitating agents for basic dyes. Lakes produced with Tamol NN, or Katanol, are somewhat brighter and faster to light than similar lakes made with tannate of antimony.

Fanal Dyes-These were produced originally about 1914, but it is only since the War that their use has reached substantial proportions. The original Fanal colours were offered as soluble dyes, which were precipitated with barium chloride on to a suitable base, e.g. Alumina or Alumina-Blanc Fixe. They were brighter and slightly faster than the ordinary types of basic lakes, but their very high price when first introduced precluded their extensive use. Since that time, however, they have been gradually improved, and, chiefly due to the enterprise of one British firm, a complete range has been offered in pigmentary form. These concentrated colours have a very high colour value. They are ready for use either after dry-grinding them with the base, or by adding a suitable amount of base to the paste colours, and even when reduced to the extent of 5 parts to 95 parts of base, they are still reasonably good colours, and possess excellent fastness to light. The concentrated Fanal colours are prepared from highly concentrated basic dyes by pre- cipitation with a complex acid, e.g. phospho- tungstic acid, phosphomolybdotungstic acid, or a phosphotungstic acid containing a small amount of vanadium. They were first intro- duced in this country about 7 years ago and created quite a sensation, since it was demon- strated that the most delicate shades of excel- lent fastness to light could be obtained with them. They are comparatively expensive pigments, but when colour value is taken into consideration the cost is not higher than that of a very large proportion of the more fugitive basic lakes. They have a certain flatness when

, lung 19341 WHITAKER--“PIGMENTS AND LAKE COLOURS AND THEIR APPLICATIONS” 173

rubbed out in oil; this is a disadvantage in some trades, but where colour value, brilliancy of undertone, and permanency me required, these colours satisfy most requirements.

As already indicated, although these Fanal and Fanal Substitute colours have extremely good fastness to light, and although the fastness and strength properties have been considerably improved since the concentrated range was first introduced, printing ink manufacturers in par- ticular are still asking for colours similar in shade and strength, but with even greater fastness to light. Attempts have been made to introduce certain other metals into the complex and the author understands that a quadruple salt has been prepared, but the results obtained do not appear to justify its preparation. The present range can be increased in strength very considerably at the expense of fastness to light and vice ver8a. The Fanal range of colours is suitable for the manufacture of printing inks and to a lesser extent for use in the paint trade; the colours give exceptionally fine results when reduced on suitable substrata for pulp colours in paper surfacing work. It is understood that one or two paper manufacturing firms in Britain are actually using these colours in dyeing paper in bright colours of good fastness to light. Traces of alkali tend to break up the complex acid in these colours, so that great care should be taken to ensure that they are used on inert bases. There is not sufficient alkali in the binding agent used in paper coating work, how- ever, to break-up the structure of the “Fanal acid”.

Certain Indanthrene dyes may be used either a8 straight colours or when reduced on a suitable base; they are much faster to light than Fanal colours, but their very high price precludes their extensive use. They have the additional value of being stable under almost any condition.

Reverting to the lakes from basic dyes, it should be mentioned that they are used chiefly for the manufacture of printing inks, typewriter ribbons, carbon papers, cellulose enamels, pulps in paper surfacing work, and to a small extent in the paint industry.

ReJEex Blue Lakes-These are very interesting colours, owing to their high bronzing properties when incorporated with media, such as litho- graphic varnish. Reflex Blue is prepared from Alkali Blue by precipitation with sulphuric or hydrochloric acid in the presence of lead acetate. The lustre of the finished product is usually helped by the addition of a little Turkey Red oil or an oil soap. In some cases, the blue, which is then, of course, the free colour-acid, is washed free from acid, filtered and dried; the best possible results are obtained by stirring a water-paste containing 20-25% solids in a dough mixer with a proportion of lithographic varnish. After a few hours, the water begins to sepafate. This is removed, the blue lake taken out of the mixer and finally finistied in a three-

roll, or preferably a “Buhler” mill in order to remove all tpaces of water. The straight product is then ready for use in making printing inks, or as is usually the w e , for topping bronze blues and blacks.

Lakes from Acid Dyes-Quinoline Yellow is an example of this group. The lakes are usually prepared by dissolving the dye and precipitating on an Alumina-Blanc Fixe substratum.

soluble-and slightly soluble acid dyes for lake making are certain types of azo dyes. Examples of soluble acid dyes are the Acid Scarlets and Oranges. The lakes are prepared usually by dissolving the dyes in water and co-precipitating in the shape of a 20% lake with Alumina or Alumina-Blanc Fixe. These colours are cheap and are sold in pulp form to paper coating manufacturers; they give bright shades which have good fastness to polishing, but only poor to moderate fastness to light.

Pigment Scarlet 3B is an important product. The parent soluble dye is prepared from anthranilic acid and R salt. The c010~1r, when converted into lake form, is a very brilliant product of very good fastness to light ; it is used in the paint and printing ink trades. Examples of partially soluble azo dyes are Lithol Red, Lake Red C, Permanent Red 4B, etc. These are pre- cipitated either with barium or calcium chloride, in the presence or absence of a substratum and usually in the presence of a dispersing agent or extender. In some w e s , e.g. Lithol Red, the lake maker is able to obtain much brighter and stronger lakes by sttlrting with the intermediates used in preparing the dye, but it is necessary to exercise rigid technical control of the process. Generally, the calcium aaltEl of the dyes already mentioned are faster to light than the barium salts, whilst the manganese salts are faster still, and the shade varies from a yellow under- tone in the cam of the barium salt to a bluish undertone with the manganese salt. With regard to the consumption of the lakes from partially soluble dyes, it may be stated that Lithol Red is still in the forefront owing, no doubt, to its high colour value and comparative cheapness, although its fastness to light is limited. Similar remarks are applicable to Lake Red C, which is less fast when converted into its barium salt. Lakes prepared fiom Lithol Rubine or Permanent Red 4B are faster than those prepared from Lithol Red, but are by no means permanent. “Lithol” lakes and Perma- nent Red 4B lakes, paxticularly the former, are used extensively in the paint trade; also in the printing ink and linoleum trades, and for paper coating work as pulp colours in conjunction with a suitable baee.

Insoluble Azo Pigrnenbs-Another class of monoazo dyes includes Helio Fast Red, Permanent Red R, and Permanent Red 26. These are insoluble in water and are used directly

Perhaps the most important of

174 NOTES OF THE MONTH [Jut18 1934

as pigments. Great strides have been made since the War in the manufacture of closely- related dyes possessing good texture and strength, and excellent fastness to light. Amongst yellows which come in this category are the Hansa Yellows. The members vary in colour from a bright primrose to a pale orange; some of them are pyrazolone derivatives. They find their chief uses in the paint and rubber trades, but have other outlets. The Hansa Yellow pigments are used in the pro- duction of paints and printing inks, and for better classes of paper coating work where extreme permanency is required.

The possibilities of using pigment colouring matters and concentrated toners in paper coating are well worth consideration by paper manufacturers, the requisite “bases” being added by the users as required. In this way, a wide range of different shades could be obtained from one colour and the practice would be an economical one. A few nitroso compounds are available in the form of pigments, e.g. Pigment Greens B and 3B.

Naphthol Green B needs to be converted into a lake by precipitating with barium chloride. It possesses excellent fastness to light, but un- fortunately it bleeds to some extent in water. When the new Bank of England Treasury ?X notes were introduced some years ago, Naphthol Green lake was used, but there were many complaints from those handling these notes daily that the colour rubbed-off easily. This defect is not so pronounced with the modern type of this colour, but the results are by no means perfect.

Pigment Greens B and 3B are extensively used in paint, dry and oil-bound distempers, and also in rubber. They have quite good fastness to light, but are not so bright as the Fanal Greens.

The colouring matter, which has long been accepted as this country’s standard for maximum fastness to light is Madder Lake. Originally this was prepared from the natural colouring matter extracted from madder root, but it is now made chiefly from synthetic Alizarin.

The lake usually is prepared in a wooden vat by boiling Alizarin with a solution containing an aluminium salt, sodium phosphate, a calcium salt and a dispersing agent, e.g. Turkey Red oil. It is considered that the permanency of the lake

is improved by heating the mixture in an suto- clave for some time. The Alizarin lakes are very transparent, but the self-colours ground in oil are not particularly bright when compared with some of the pigment oolouring matters. In spite of these facts, however, and on account of their stability and permanency, the lakes are used extensively in paint manufacture and as artists’ colours.

Although tremendous strides have been and still are being made in the production of brighter and faster-to-light organic colour lakea, there remains room for improvement. In this con- ncxion it seems as if more depends upon the dye manufacturer than upon the actual lake maker. Research work could be concentrated with advantage an the anthraquinonoid type of dye in an effort to reduce the cost, and to endeavour to produce a complete range of colours of varying shades.

Some experiments carried out by the author a few years ago with Caledon Jade Green, gave results which showed that a dispersion in litho varnish was considerably stronger in colour value than the same concentration of Fanal Green, and certainly was very much faster to light. Prints of the dye containing varying amounts of a white base were exposed for a year to daylight, and no trace of facling was discernible. It is realised, of course, that fugi- tive colours will still have to be used for 801130

considerable time owing to their low price, as some of the uses to which colours are put, entail only exposure for possibly a day at the outside.

With regard to plant, there is a divergence of opinion as to whether square vats or circular vats produce the best results in colour “strik- ing”. Experience seems to show, however, that there is little difference, providing the agitation is efficient. Means of dealing with a colour after it is “struck” are usually confined either to gravity or vacuum filters, or filter-presses.

There are varied opinions also as to the best method of drying colour lakes, i.e. with direct heat, hot-water or steam pipes, or hot air. The last is by far the most economical method.

The author desires to thank James Anderson & Co. Ltd., for the facilities which they have afforded in the compilation of this paper, and also members of the staff for their help in the preparation of the various specimens exhibited.

Notes of the Month The Jubilee Celebrations paid to the premises of‘ Messrs. Isaac Holdcn &

Preliminary Account Sons Ltd., commission woolcombem, Alston The Jubilee Celebrations of the Society took Works, Bradford.

place during Whit-week. They were inaugur- An interesting afternoon was spent a t ated on Wednesday evening, 23rd May, with Torridon, Headingley, Leeds, the headquarters a civic welcome by the Lord Mayor of Bradford of the Wool Industries Research AsRociation, by (Captain A. W. Brown, M.B.E., J.P.), followed kind invitation of Lord Barnby. Mr. F. T. by a conversazione at the Technical College. Chadwick (Vice-chairman), Dr. S. G. Barker

On Thursday morning, 24th May, a visit was (Director of Research), and M i . Arnold Frobisher