how to make a thin section

7/23/2019 How to Make a Thin Section

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How to make a thin section

Dave's methods at WWU Geology

Note: this document is online at www.davehirsch.com (under "Miscellany")

What is a thin section?

A thin section is a 30 m (= 0.03 mm) thick slice of rock attached to a glass slide with epoxy.

Typical thin section slides are 2 mm x ! mm" altho#gh larger ones can $e prod#ced. They are

generally co%ered $y another glass slide" a co%er slip also attached to the rock with epoxy. Theepoxy ideally has an index of refraction of &.'!" altho#gh o#r epoxy is slightly higher" perhaps

&.'.

The sections may $e left #nco%ered for chemical analysis on the * or electron micropro$e. +f

so" temporary co%er slips may $e weakly attached with glycerin.

Thin section making equipment

There are fi%e main tools yo# will #se, The sla$ saw" the trim saw" the grinder" the c#t-off saw"

and the lap wheels. o# will want a harpie-type permanent marker" some li/#id paper and afine-tipped permanent marker.

arnings, Things yo# can damage in the la$

1e s#re when yo# #se either the c#t-off saw" or the thin section grinder" that the $ottle is

less than half f#ll of water. +f it gets too f#ll" water can $e s#cked into the $#ildings%ac##m system. This wo#ld $e $ad. ont do this.

1e s#re to clean and dry the grinding wheels promptly after yo# finish #sing each one" or

they will r#st rapidly. +nstr#ctions for this are gi%en $elow.

1e s#re to #se the correct grit for each grinding wheel. 4rom left to right" they get finer

and the grit n#m$ers get larger, &20" 2!0" !00" 00.

Making your thin section

(5ote, yo# can click any image for a greatly-

enlarged %ersion)


2/16

This g#ide is descri$ed in steps" withphotos of a sample rock shown alongside

as it #ndergoes the %ario#s steps.

tep 6ne7, 8repare the glass slide

7o# dont act#ally ha%e to do this first. +n fact" + often do this for awhole $#nch of slides at once" then #se them as needed.

The glass slide yo# will gl#e the rock to

m#st $e flat in order for the rock sectionto end #p with a constant thickness. +n

order to achie%e this yo# need to 9frost9

the slide" which accomplishes two goals,

&. :emo%es the thick spots on theslide

2. Ad;#sts the slide face to $e parallel

to the grinding wheels face.

To do this s#ccessf#lly" yo# need to $ea$le to keep the slide in the same

orientation $oth which yo# are frosting it

and later when yo# are grinding it. +

accomplish this $y grinding off a cornerof the slide #sing the 2!0 grit grinding

wheel.

rinding

wheels. heels ha%e

partic#lar a$rasi%es,

rightmost wheel is &20

grit" then 2!0 grit(open)" then !00 grit"

then 00 grit . >lassslide corners are

gro#nd #sing the 2!0

grit wheel.

4ig#re 2. 8#tting wateron spinning wheel.

4ig#re 3. 8#tting 2!0-

grit a$rasi%e on

spinning" wet wheel.

4ig#re !. >rinding the

corner of a glass slide

on the wheel.

4ig#re '. >lass slidewith a corner gro#nd

off. 5ote reflection -

its not yet frosted.


3/16

wheel (if yo# #se the right side"which is mo%ing towards yo#" it

may kick o#t of yo#r hand).

'. 6nce a small amo#nt has gro#ndaway" yo#re done. lean allgrit

off the slide in the sink.

. o# m#st clean the wheel

promptly" or it will r#st. The nextsection descri$es how.

leaning the grinding wheel

o# m#st clean the grinding wheelspromptly" or they will r#st. . ry the spinning wheel with thehair dryer #ntil its totaly dry.


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+. lean the $ench top that holds thewheels.

tep Two, 4rost the glass slide

o# will now 9frost9 or grind the glass

slide to flatten it o#t and ro#ghen the

s#rface so the epoxy can $ind well. Toaccomplish this" yo# m#st always place

the slide on the grinder in the same

orientation. (+ always p#t the slide on so

that the c#t-off corner points #p andtowards me).

&. T#rn on the water to the grinder.

2. 4ind a fairly clean slide (not

frosted) and place it on the slideholder of the c#t-off saw (wet it if

it doesnt stick). This is $eca#se

the two de%ices share a %ac##msystem" and the one not in #se

m#st ha%e a slide to create a seal.

3. ipe clean the slide holder of the

grinder. Any grit will prod#cescratches on the finished section.

!. 8lace the section on the holder of

the grinder.

'. T#rn on the %ac##m (the %al%e is$etween the two instr#mentsB its

on when it points away from the

wall). heck to see that the slide is

firmly held.

. T#rn the control towards yo# #ntil

it reads a$o#t ?0. (This is co#nter-

clockwiseB yo# sho#ld see the left

part of the grinder mo%e awayfrom the right part which holds the

4ig#re &0. #t-off saw

(left) and thin section

grinder (right). 5ote

that water controls are$etween sink and c#t-

off saw" and %ac##mcontrols are $etweenthe two.

4ig#re &&. lide on

grinder showingposition incl#ding

gro#nd corner.

4ig#re &2. 8lacing

slide on grinder for

frosting. 1e s#re slide

rests against the pins"and place it on the

holder with the

%ac##m t#rned off.

4ig#re &3. >rinder

control with n#mericalga#ge.

4ig#re &!. lidemostly frosted" $#t

with #nfrosted portion

at top.

4ig#re &'. lide

completely frosted.


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grinding wheel).

?. T#rn on the motor.

@. hile mo%ing the slide $ack andforth" slowly t#rn the control

clockwise #ntil the slide $egins tocontact the grinding wheel.

. 5ote the n#m$er (on the control)

at which contact is made.

&0. hile still mo%ing the slide $ackand forth" ad%ance the control

wheel grad#ally a$o#t three ticks

from the contact %al#e. At thispoint" grind for a while witho#tad%ancing the wheel while mo%ing

the slide $ack and forth" to ens#re

complete and e%en grinding.

&&. T#rn off the %ac##m and press the

%ac##m release %al%e (the $lack

t#$e from the slide holder

connacts to itB it is pressed towardsyo#). hen the hissing stops"

remo%e yo#r slide from the holder.(Try not to drag it" or it may getscratched).

&2. ry it off and see if its all frosted

e%enly. +f not" repeat the a$o%e

steps #ntil it is. o# sho#ld notneed more than fo#r ticks or so.

&3. 6nce its all frosted" make a note

of the position at which yo#

stoppedB yo#ll need it later. This%al#e is the Cero-thickness

position" the position at which the

grinding wheel contacts the glassslide.


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tep Three, *ark yo#r rock

o# need to decide where yo# will c#t

yo#r rock. This matters" especially with

rocks that ha%e a fa$ric. o# generallywill want to c#t a thin section on a plane

perpendic#lar to any planar fa$ric" $#t for

partic#lar p#rposes yo# may want thinsections in other orientations. *ark a line

on the rock with the harpie.

4ig#re &. :ock priorto c#tting. 8encil for

scale. 5ote that this

rock was not marked

$efore c#tting" $#tnormally it wo#ld $e.

tep 4o#r, #t the sla$

Dsing the sla$ saw in the $ack of theroom" yo# will c#t a sla$ from yo#r rock

along the line yo# marked.

&. 4irst clamp the sample in theholder so that the line is parallel to

the saw $lade" sticking o#t of the

holder. o# do not make yo#r firstc#t along this lineE

2. 4ind crank handle and attach to

s/#are protr#sion on tray. indthe tray a$o#t && t#rns away fromthe saw $lade. There is some

hysteresis" or 9slop9" so dont

co#nt crank t#rns where the trayisnt mo%ing. :emo%e the crank

handle.

3. lose the co%er" making s#re the

sides and $ottom are t#cked insidethe lip.

!. *ake the c#t. 4irst t#rn the switch

on to get the $lade mo%ing" then

t#rn the kno$ #ntil the weight$egins to fall.

'. 6nce the c#t is done (yo# can hear

it)" t#rn the $lade off and stop the

4ig#re &?. la$ saw.

5ote location for crankin $ottom center.

4ig#re &@. la$ sawcontrols. T#rn kno$ to

mo%e rock

intoFthro#gh $lade" and

switch start $ladet#rning (only t#rn on

with co%er completely

closedE).

4ig#re &. :ock ready

for first c#t. 5ote thatit sticks o#t extra far to

allow for second c#twitho#t remo%ing fromclamp.

4ig#re 20. After first

c#t. 5ext" close kno$"

p#ll tray $ack fromsaw" then mo%e tray

towards $lade a$o#t &&t#rns of the crankhandle.


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weight mo%ing $y t#rning thekno$ away from yo#.

. 8#ll the tray $ack to the $eginning"

and #se the crank to wind the$lade $ack to yo#r line" && real

t#rns (where the tray is mo%ing).

?. :emo%e the crank handle" and

close the co%er.

@. *ake the next c#t as yo# did thefirst. These two c#ts sho#ld $e

parallel planes a$o#t @-&0 mm

apart. The sla$ sho#ld fall onto the

catch tray $ehind the $lade.

4ig#re 2&. :eady forsecond c#t.

4ig#re 22. After

second c#t, sla$complete (piece lying

on catch tray at left).

lean #p the sla$

&. 4irst wash the sla$" the lefto%er

rock" and the first c#t piece (if

theres eno#gh to sa%e) to remo%e

any oil and grit from the sla$ sawprocess.

2. 5ext (while the rocks are drying)

set the lefto%er rock and the first

c#t piece on a paper towel to dry"$#t mark the sample n#m$er on

the towel. +ts %ery easy to mix #p

specimens at this point" $eca#seyo# may ha%e needed to c#t

thro#gh the n#m$er pre%io#sly

marked on the rock. Also" the firstc#t piece likely has no n#m$er.

6nce these are dry" re-mark them

with the sample n#m$er. + #seli/#id paper and an india ink pen"

followed $y nail polish once its

dry.

4ig#re 23. ashing oil

and dirt off the rocks

after sla$ c#tting.

4ig#re 2!. rying

speicmens with sample

n#m$er written on thepaper towel .

tep 4i%e, #t the chip


8/16

o# need to red#ce the siCe of the sla$ toslightly smaller than a thin section. 4or

this yo# will #se the trim saw against the

$ack wall of the room. o# need to

caref#lly decide from what part of the sla$yo# want to c#t the section.

&. o# will #se a special rock-c#tting

$lade which is made of metal withdiamonds em$edded in it.

ssentially" s#ch $lades are narrow

grinding tools. o# can e%ensafely p#t yo#r finger on it as it

mo%es (if it is l#$ricated with

water)" howe%er yo# sho#ld not

p#t yo#r fingernail on it.

2. o# sho#ld wear eye- and ear-

protection gear when #sing this

saw.

3. tart the water #sing the %al%ea$o%e and to the right of the saw"

and start the $lade #sing the switch

to the right.

!. o# ;#st p#t the sla$ on theplatform and mo%e it into the

$lade. o# can #se a glass slide to

get the siCe correct (the chipsho#ld $e slightly smaller than the

slide).

'. After c#tting the chip" the side

from which the thin section will $ec#t m#st $e polished to remo%e

marks from the saw $lade. 4or

$est res#lts yo# can grind on eachof the fo#r wheels" $#t a #sea$le

section will res#lt from ;#st

grinding on the seccond (2!0 grit)wheel.

. As a$o%e" clean the grinding

4ig#re 2'. These

$lades are safe to

to#ch as long as theyare l#$ricated" $#t

dont p#t yo#r

fingernail on it.

4ig#re 2. The

platform mo%es" soyo# ;#st p#sh the sla$

thro#gh the $lade.

4ig#re 2?. 4inal c#t for

the chip.

4ig#re 2@. >rindingthe chip will remo%e

any saw marks from

the c#tting.

4ig#re 2. ashing the

chip.


9/16

wheel when yo# are done with it.

tep ix, >l#e the slide to the chip

5ext" yo# attach the frosted side of theslide to the side of the chip yo# ;#st

gro#nd down. o# need to ens#re a

constant thickness of epoxy across thesection" or when yo# grind the section

down" one end will $e thicker than the

other.

&.


10/16

o These materials now m#st

$e well-mixed" $#t whilecreating as few $#$$les as

possi$le. +n order to

achie%e this" + drag thecoffee stirrer in a sin#o#s

pattern first in one

direction" then in the samepattern rotated 0 degrees.

!. 6nce the epoxy is well-mixed"

spread a few drops across the top

(polished side) of the warmedchip.

'. *any rocks are poro#s (e%en somethat yo# might not expect) and yo#

m#st let the epoxy penetrate f#lly"or the thin section will not s#r%i%e.

o" spread epoxy" then wait for it

to soak in (' min#tes) then spreadmore epoxy. :epeat #ntil no more

epoxy soaks into the chip.

. 8lace the slide" frosted side down

on the epoxy. +ts $est to p#t one

side down" then let the other sidefall to a%oid trapping $#$$les.

?. *o%e the slide aro#nd with yo#r

finger or a pencil eraser. This wills/#eeCe o#t extra epoxy to achie%e

a constant thickness" and if yo#

work at it" yo# can remo%e most$#$$les this way as well. hile

doing this" $e s#re that the sample

n#m$er gets coated with epoxy.

@. Get this sit to c#re. heck itperiodically for the first '-&0

min#tes to $e s#re the slide has not

slid off the chip.

. The epoxy will c#re in a$o#t 20-30 min#tes. o not take the next

4ig#re 3. 8lacing

slide on chip" frosted

side down.

4ig#re 3?. *o%ing

slide aro#nd to expel

$#$$les and extra

epoxy" and coat samplen#m$er.


11/16

step $efore that.

tep e%en, #t off the chip from theslide

5ow yo# ha%e a rock chip epoxied to a

glass slide. o# will next c#t most of the

chip off" lea%ing a thin slice attached.

&. 8lace a $lank glass slide on thegrinder to $lock the %ac##m.

2. T#rn on the water to the c#t-off

saw.

3. 8lace the slide on the c#t-off saw(note direction of gro#nd corner)

and t#rn on %ac##m to hold it. 1e

s#re edges of slide are lodgedagainst pins in holder.

!. T#rn on saw motor.

'. Dse the handle to mo%e the chip

into the $lade. >o %ery slowly" or

yo# can $reak yo#r slide and ha%eto start o%er.

. 6nce the chip is c#t off the slide"

retrie%e the chip from the water

tray and set it aside (it will likelyneed to $e la$eled with the sample

n#m$er).

?. T#rn off the %ac##m" and saw

motor.

@. Dsing the $#tton (as with the

grinder - see a$o%e)" $reak the

%ac##m. 6nce the hissing stops"remo%e yo#r slide from the saw.

4ig#re 3@ . lide withchip mo#nted in c#t-

off saw.

4ig#re 3 . lowlyc#tting off the chip

from the slide.

4ig#re !0 . hip nearly

c#t from slide.

4ig#re !& . hip and

slide separated.


12/16

. :inse yo#r slide to remo%e anyparticles.

tep ight, >rind yo#r slide to the correct

thickness

o# m#st now grind away m#ch of the

rock that remains on yo#r slide" $#t not allof it. This is the step in which most thin

sections go $ad. The key is, go slow"

especially near the end.

&. 8lace a $lank glass slide on thec#t-off saw to $lock the %ac##m.

2. T#rn on the water to the grinder.

3. T#rn the control towards yo#

(co#nter-clockwise) a f#ll rotationto Cero.

!. 1e s#re the slide holder and the

slide are clean and free of any grit

or particles.

'. 8lace the slide on the grinder(maintaining the same orientation

#sing the corner yo# notched).

. T#rn on the %ac##m and grinder

motor.

?. *o%ing the slide $ack and forth

with the handle" grad#ally ad%ance

the control #ntil the slide contacts

the grinding wheel.

@. hile mo%ing slide $ack and forth

across the grinding wheel with the

$lack handle" grad#ally ad%ancethe control #ntil yo# reach a point

a$o#t &' ticks $elow yo#r 9Cero

%al#e9 (see step 2).

4ig#re !2 . Dngro#nd

slide mo#nted ingrinder holder.

4ig#re !3 . *o%ing

slide across grinding

wheel while ad%ancingcontrol (with right

hand).

4ig#re !! . hecking

the slide thickness#sing the microscope.

4ig#re !' . H#artC in a

thin section" way toothick.

4ig#re ! . H#artC in a

thin section" still fairlythick.

4ig#re !? . H#artC in a

thin section" still a $itthick.

4ig#re !@ . H#artC in a

thin section" now too

thin. At this point"m#ch of the remaining


13/16

. :emo%e the slide (t#rn off the%ac##m" $reak the %ac##m with

the $#tton" then remo%e the slide)

and see if yo# can identify any

minerals in the section.

o +f yo# can" then proceed

slowly #ntil those minerals

achie%e the correct

maxim#m interferencecolor (e.g." /#artC sho#ld

show a maxim#m

interference color of a palestraw yellow)

o +f yo# cannot" thenad%ance one tick at a time

#ntil yo# can identify a

mineral. +f yo# are within 'ticks of yo#r Cero %al#e"

and yo# still cant identify

anything" stop and ask

someone who knows morethan yo#.

o >o slow" especially when

yo# are close to the correctthicknessE +ts /#ite easy to

go from slightly too thickto slightly too thin (or

gro#nd completely away)"even without advancing

the position control at all!

Tro#$leshooting

o Warning, *ost sections

fail at this stage $eca#seyo# are grinding too fastE

:emem$er" any time thegrinder makes noise

against a slide" yo# are

remo%ing rock. o# oftendont ha%e to ad%ance the

section has $een

gro#nd away.


14/16

wheel at all to ;#st grind asmall thickness away.

o +f yo#r section comes o#t

with the minerals allcracked, you were

grinding too fast.


with the edges thin and the

center thick, you weregrinding too fast.


thick on one side and thin

on the other" yo# eitherdidnt frost the slide well"

or there was an #ne%en

epoxy layer.

tep 5ine (%ersion &), Add a co%er slip

+f yo# do not expect to perform chemicalanalysis on yo#r minerals in this thin

section" yo# sho#ld add a co%er slip toprotect the section from damage" andincrease the clarity o$ser%ed in the

microscope. This process is a simple one,

&. *ake s#re the section is clean and

free of grit or dirt.

2. 8lace it on the hot plate.

3. *ix #p a small $atch of epoxy and

hardener.

!. 8lace a small drop of epoxy on the

section.

'. rop a co%er slip on the drop.

. *o%e it aro#nd to expel $#$$les

4ig#re ! . 8#tting adrop of epoxy on the

gro#nd slide.

4ig#re '0 . ontainerfor co%er slips.

4ig#re '& . ropping aco%er slip on the slide.

8#t one end down firstin order to pre%ent

$#$$les.

4ig#re '2 . *o%ingco%er slip to spread

epoxy and expel$#$$les.


15/16

and f#lly coat the section.

?. Get it c#re.

@. After it has c#red" there may $eextra epoxy on the top" sides" or

$ottom. o# can remo%e this" very

carefully" with a raCor $lade.

tep 5ine (%ersion 2), 8olish for lectronmicropro$e F *- analysis

+f yo# plan to perform chemical analysis

on yo#r minerals" then yo# need to polish

the section m#ch $etter than the grinderpolishes it. This is $eca#se these analysis

tools re/#ire a flat" smooth s#rface at the

micrometer scale. o# perform thispolishing step #sing different tools in a

different room.

The key diffference for o#r p#rposes here

is that yo# sho#ld stop grinding when thesection is still a little $it thick" $eca#se

yo# will $e remo%ing material d#ring the

polishing process.

The polishing apparat#s is located on thegro#nd floor" at the other end of the

$#ilding (near the I:).

(4#ll instr#ctions for polishing may $eadded to this doc#ment in the f#t#re. 4or

now" ask a knowledgea$le #ser for help).

tep Ten, lean #p the place

o# m#st clean the la$ thoro#ghly when

yo# are done #sing it. o# may store

samples in progress in one or more traysclearly la$eled with yo#r name and the

date. These trays are placed in the lower4ig#re '3. rying off 4ig#re '!. 6iling the


16/16

ca$inets in the thin section la$ room" or(for grad st#dents) in the ca$inets in the

center of the ad;acent room.

&. *ake s#re that the grading wheelsare clean and dry (see instr#ctions

a$o%e).

2. ompletely dry off the dark metal

section holders on $oth the c#t-offsaw and the grinder.

3. 4or each of those two tools" spread

some oil on a paper towel" and

coat the dark metal portion

thoro#ghly with oil" then place theoiled paper towel #nderneath the

section holder.

!. mpty o#t the water from the%ac##m $ottle (co%ered with tape).

'. 8lace any epoxy stirrers crosswise

on the epoxy holder so that when

the epoxy dries" $oth can $ere#sed.

. *ark yo#r name in the log sheet.

?. T#rn off the lights and close the

door when yo# lea%e.

the section holder. paper towel.

4ig#re ''. 6iling thesection holder.

4ig#re '. Tool dried"

oiled" and paper towelplaced for storage.

4ig#re '?. :emo%ingt#$ing from %ac##m

$ottle.

4ig#re '@. mptyingthe %ac##m water

$ottle.

4ig#re '. poxy

stirrer and tray storedfor c#ring and re#se.

4ig#re 0. 4illing o#tthe log sheet.

how to make a thin section

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