WATCH CASING

MATERIALS• Pocket watch cases were traditionally made out of plated base metal or silver in low to mid range

watches and High end watches were made from precious metals.

• Plated cases feature marks such as rolled gold, gold filled and gold plated and often the amount in thickness they were plated to. Often times the thickness of the plating was rated in number of years that it could be expected to last.

• Cases were dust proof but never water resistant.

MATERIALS

• Hallmarks on cases indicate who manufactured the case, not who made the whole watch. Often times case, dial and movement were sold separately at the jewelry store and assembled on site.

• Gold used is 10K (41.6% Au), 14k (58.3% Au), and 18k (75% Au) in America with different carat content varying by nation of origin. 24k gold is never used because it is too soft for practical use.

• Coin silver (90% Ag) was used in America exclusively. Sterling silver (92.5% Ag) was used elsewhere and is still the standard for quality silver pretty much worldwide

• Platinum 950 (95% Pt) is very rare and expensive in addition to being much harder to work with. It is reserved for only the finest of timepieces.

MATERIALS• Watch cases used to be made out of plated base metal but now Steel has become the

standard. Some very cheap watches are still made out of base metal.

• Watches are still gold plated to keep them affordable but steel is usually the underlying metal used.

• Stainless 316L steel is used in most high end watches with the exception of Rolex who uses 904L steel.

• Electroplating has been largely replaced with PVD or Physical vapor deposition where elements are bonded to the metal in a gaseous form.

• Another coating some companies use is ADLC or Amorphous diamond like coating in which a 2-3 micron thick coating of super hard carbon is “grown” on the case and acts like a protective shell. Its black metallic appearance is also popular.

• Many companies are using different more exotic materials starting in the last decade. Materials used include ceramic, titanium, tungsten, bronze, aluminum, carbon fiber, forged carbon, wood and new alloys that are stronger and lighter.

CASING RINGSOften times the movement isn’t made to the exact size of the case. When this happens the

manufacturer installs a casing ring to make up the difference between the movement and the case. These rings add a level of cushioning that helps protect the watch from shocks. In the case of metal casing rings, ferrous metals are used to shield the watch from magnetic fields. Some watches even have an iron shield that covers the back of the movement under the case back to add another layer of magnetic resistance.

BEZELSBezels can provide important measurements and scales used in a variety of sports and

professions. Bezels can also be just for looks. Sometimes they hide seals and sometimes they create the actual seal through friction. Here’s a sampling of some more common bezel types.

A tachymeter bezel is a fixed bezel with a non-linear scale that measures the occurrence of an event over an elapsed time. Most commonly this is used for measuring average speed per mile when driving or rate of units of production.

BEZELS

A slide rule bezel is a bezel with 2 logarithmic scales, the inner one fixed, the outer rotating, both with non-linear scales. The number of computations that can be done with a slide rule is staggering. These bezels are often present on pilots watches so fuel consumption can be calculated. Common uses for the professional and non-professional user alike are conversions (mph / kph, Fahrenheit / Celsius etc…), Calculating percentages, trigonometry, roots and powers, base-10 logarithms and exponents, and simple arithmetic.

BEZELS

A GMT or UTC bezel rotates and has 24 individual markers each representing a time zone. When combined with a fourth hand that makes one revolution per day, the bezel allows for the reading of local time as well as home time. This is a common feature for aviation watches. In addition to the GMT or UTC hand, a bezel featuring major cities in each of the 24 time zones can be used making the watch a world timer.

BEZELS A telemeter bezel is fixed bezel graduated in distance (Kilometers or miles). It is used to calculate the distance of an occurrence based on the sound it emits. This was used in many military watches. A soldier could hear gunfire and see where it was happening then use their watch to calculate the distance and give a report based on the findings. It can also be used to calculate how far away lightening is based on the difference between the flash and the sound of thunder.

A pulsometric bezel or a bezel with a pulsometer scale, is graduated in beats per minute and has an indication of how many beats are to be counted to get an accurate reading. These are used by medical professionals to find heart rate. A short series of heartbeats is taken when the stopwatch is started. Then by reading the position of the second hand in relation to the bezel, an average beats per minute can be derived from the chart on the bezel.

BEZELS

The divers bezel is a rotating bezel that is used to measure elapsed time. While it can be used for general purposes to measure any amount of elapsed time by turning the bezel so the “0” point it aligned with whichever hand is appropriate for the period desired, it was originally designed for divers to track how long they have been on a dive and how long they have until they need to begin their assent. The last 15 minutes are generally graduated in increments of one minute to accurately track the rate of assent to prevent decompression sickness.

BEZELS

Bezels can be a purely decorative aspect of the watch as well. Often times they are set with precious stones or have ornate patterns.

CRYSTALSAcrylic / Plastic

Before the mid 80’s plastic was almost universally used with the exception of Lepine pocket watches. Plastic has the advantage of being very hard to shatter. While it scratches fairly easily, the scratches can be buffed or polished out a number of times before the crystal requires replacement. Crystals made of plastic are far easier to manufacture and therefore allowed for a large variety of shapes and styles compared to mineral and sapphire glass.

• Omega uses Hesalite, a proprietary plastic, for the crystal on their speedmaster chronograph for use in space because it was necessary to have a crystal that won’t shatter and create micro fragments that could damage instruments.

CRYSTALSMineral glass

Mineral glass crystals are generally only used in lower priced watches. They are less expensive materially and less expensive to manufacture. While not as hard as sapphire, they are equally as prone to shattering and chipping. The only benefit to the consumer is price.Sapphire crystal

Sapphire or corundum is grown in a lab in boules. It is 3rd in hardness on the Mohs mineral hardness scale with only moissanite and diamond surpassing it. Because of the difficulty present in machining such a hard material as well as the material cost it is quite a bit more expensive than mineral glass. Especially if it is any shape but a simple flat cylinder. It is becoming more of a standard in the watch industry where only 10 years ago it was used only in the most expensive watches.

CRYSTALS• Both Plastic and glass crystals are either frictioned in or glued in. However, glass requires a gasket to

achieve a friction fit whereas plastic crystals can achieve a snug fit without a gasket because of their softer, more flexible properties.

• Crystals can be glued in using an epoxy or crystal cement. Some manufacturers use a UV cement that only hardens when exposed to a very strong ultraviolet lamp.

• Many watch companies have started putting a pane of glass on the caseback of the watch to allow a view of the movement. While this is a great selling feature and very well liked by consumers it is an additional point at which water can penetrate the case and can increase the likelihood of leakage. For this reason most certified dive watches do not have exhibition backs.

• Some crystals feature an anti-reflective coating that enhances legibility of the dial. This coating can be on the inside, outside or both. It does have the drawback of being very easy to scratch so it often times necessitates the crystal being replaced at service due to the impracticality of recoating.

CASE BACKS There are four methods of sealing the backside of watch cases.

Snap on: These cases are generally found on inexpensive watches and provide the bare minimum of water resistance. They attach via a geometric connection with a lip on the inside of the case back that snaps into a groove cut into the case. A rubber gasket creates the seal. If the caseback becomes flexed at all the case can lose its ability to fit properly or make the case unable to become water resistant again.

Friction fit: Similar to the way glass crystals friction in to a gasket on the front of the case, these case backs use a hard nylon gasket to create a friction joint between the case and back. If the gasket is damaged, greased or installed incorrectly the back will not be able to friction properly. This method creates a seal slightly better than that of a snap on case back but it isn’t a marked improvement.

CASE BACKSScrewed down: The case back is attached using a series of

screws that compress a rubber gasket between the case and back. The strength of the fit as well as the water resistance varies widely depending on the number of screws as well as their size and the size of the gasket. This method is usually found on dress watches that feature a lower water resistance rating but are also used in watches with water resistance exceeding 200m. Screws can back out due to not being properly tightened and moisture can penetrate the case due to uneven pressure if the screws aren’t uniform in their torque and care must be taken to ensure they are screwed down evenly and Loctite used when appropriate. Many manufacturers use this style of case back in conjunction with specialized screw heads and corresponding screwdrivers to prevent non-authorized individuals from entering the watch.

Screwed in/on: This method allows for the maximum of water resistance due to a large effective sealing area and a very heavy even torque being applied. Pretty much all 200m + water resistant watches use this method. Many manufacturers use this style of case back in conjunction with specialized case back dies to prevent non-authorized individuals from entering the watch.

CASE BACKS

• In some older watches, primarily made in the 60’s and 70’s, There was actually not a case back at all! These are called one piece cases. The movement is installed through the front and the crystal or bezel must be removed and a two piece stem is used so that the movement can be lifted out without the need to release the setting lever.

CROWNS AND TUBESCrowns come in a wide variety of styles but the functional principles are generally

the same across most watches. All crowns fit onto a tube. The thinner diameter friction fits into the case and is adhered with Loctite. This creates a strong water sealed bond. The crown then fits onto the tube. An O-ring gasket in the crown creates a water seal against the outside of the tube

Screw down crowns seal under the same principle of an O-ring filling the gap between the crown and tube but they have the additional benefit of being compressed to create a much better seal. A screw down crown is a necessity on a professional dive watch. Some threaded tubes screw into the case as well. Just like with the threaded crown this creates a better water seal than a friction fit tube. The designs for threaded crowns and tubes vary quite a bit by manufacturer and often times require special tools to install and remove them properly.

PUSHERSLike crowns, pushers come in either threaded or non-threaded

types. Some use tubes that thread into the case, but the majority are friction fit with Loctite. The pusher is generally made up of a tube, a spring, at least one gasket, and the pusher itself. The pusher is either held in by a screw or a C clip. Some cheaper watches have pushers that are an assembled unit that cant be disassembled and the whole pusher is replaced with service.

Some pushers screw down to prevent them from being operated by mistake. There are a few exceptions, but in general if the pushers are operated in water the watch will almost definitely leak.

GASKETS• Gaskets typically come in two varieties. Black rubber O-rings and Nylon gaskets.

• Rubber O-rings are used in case backs, crowns, and pushers and can be either round in profile or flat and rectangular. They are available in standard round sizes but can also be formed to fit any shape of case back.

GASKETS

• Nylon or Zytel gaskets are used for case backs and crystals. Generally crystal gaskets are white but can come in a variety of other colors. Back gaskets made of Zytel are almost always red.

GASKETS• Gaskets should generally be changed with every service to preserve water resistance.

• Nylon gaskets are often a one time use gasket because the tight friction they receive from the crystal or case back permanently alters the shape of the gasket.

• Gaskets should be checked thoroughly to ensure the shape and consistency is still intact. Through aging and UV damage gaskets can become brittle and crack causing the watch to leak.

• While black rubber O-rings should almost always be greased with silicon or fomblin grease, Nylon gaskets should never be greased. If the nylon gaskets are greased it will prevents them from being able to firmly friction in resulting in crystals and case backs that pop off.

WATER RESISTANCE

What to do if there is water in your watch…

WATER RESISTANCE

…So this doesn’t happen.

WATER RESISTANCEWhat is water resistance?

The first water resistant watch made for public purchase in any quantity was the Rolex oyster watch in 1926. There were various previous incarnations for industrial and military applications made by a number of different firms but in very unique, small quantities.

Before the advent of water resistant technologies, watches were very susceptible to moisture damage from even the most minor of exposures to moisture and therefore required more frequent servicing. The ability to be around water drastically increased the versatility of watches as a tool and as a fashion accessory.

Since the invention of the water resistant watch, many advancements have been made to improve the reliability of seals and the depths to which watches can be used. Up until the 50’s it was rare to find a watch that had anything more than the very minimum of water resistance. Today, daily wear watches sport depth ratings of over 200m and the record for the highest depth rating on a watch seems to be broken every year. To date, the highest rating a watch has achieved is the Sinn UX series of watches that are tested at a depth of 12,000 meters!

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WATER RESISTANCEWhat is does water do to the insides of a watch?

If a watch has any moisture beyond the ambient moisture present in the air inside the watch the only way to guarantee the continued functionality and condition of internal parts in to fully service the watch. Many people will offer to “Dry-out” a watch with moisture by opening the back and putting it on a heater or just letting it naturally dry. This actually causes more damage to the watch. The oxidation of the steel parts in the watch occurs when the moisture is allowed to dry on the surface, therefore drying the watch out is just encouraging the rust to occur faster. By properly disassembling and cleaning the watch the moisture is being removed before it has time to do any further damage. Plus, oil and water don’t mix. The moisture will move the oils away from the important places they need to be and deposit it randomly all over the movement. This results is pivots that are badly worn and eventually fail to transmit energy.

Often times you will hear people say “Its just a little bit of condensation, its no big deal.” Any amount of moisture will cause damage to metal parts. Additionally, the paint used on watch dials is very sensitive and will cause discoloration and peeling.

“It only appears when it gets hot.” This water isn’t just disappearing when the watch cools. The air inside the watch has just heated enough to reach its saturation point so that the water goes from a gaseous to a liquid state. When it cools it will revert back to its gaseous state but it won’t leave the watch.

“It runs fine.” Sure, right now, but over time it will cause damage that will eventually stop the watch. It’s not an if, but a when. As time goes on, the rusting will get worse and eventually when it does stop working the service will be quite a bit more expensive as more parts are needed. If the dial and hands get moisture damaged you may be looking at double or even triple the price of a normal service.

WATER RESISTANCEHow to decipher water resistance ratings

Water resistance is measured in meters and the units are represented in either bars or atmospheres (ATM). 1 bar and 1 ATM both equal 10 meters. Therefore a watch with a water resistance listed as 20 bar is 200m water resistant. A watch with no specific numerical rating that just says water resistant or may have a picture of a fish, is considered the minimum of 3 bar or 30M.

On some older watches you may see “waterproof” This term was deemed inappropriate by the federal trade commission in the 1960’s because A watch cannot be said to be 100% waterproof if there are seams. Given enough time and the right conditions, any watch can be victim to water damage.

These terms can be confusing to the lay person because you would think a watch marked “water resistant 100 meters” would be able to be worn in any wet condition as long as the depth doesn’t exceed 100 meters. What this actually means in practical application is quite different. Depth ratings are regulated by ISO standards and are covered under the umbrella standard ISO 22810:2010 for water resistant watches. Watches are tested in a laboratory environment in pressurized water at roughly room temperature at a pressure equivalent to 125% of its listed depth rating. What may be the most important factor in this test is that the watch is tested in a stationary environment. The pounds per square inch exerted on a watch while stationary in still water is exponentially less than that of the psi if the watch is quickly moved like when on a wearers wrist. For reference, a watch that is rated 10 Bar is only suitable for light swimming, not diving. 30M is only suitable for light splashes and water should generally be avoided.

WATER RESISTANCEPressure testing

Watches can be tested dry or wet. Generally watches are tested dry first to ensure that they are properly sealed and then a secondary wet test is performed as a final test or to diagnose where a leak is happening

WATER RESISTANCE

Dry tests operate by sealing the watch in a very thick dome or tube. A small sensor is applied to the crystal of the watch that will detect minute deformations in the case as pressure is supplied via a manual crank or an air compressor to simulate the pressure present at a corresponding depth. As the chamber fills with air the case will steadily deform. If the deformation remains constant as the chamber fills and then stops once pressure is reached and remains in that shape for the duration of the test the watch will be considered water resistant. If a leak is present, at the point air enters the case, the case will begin to expand instead of contract as the case inflates. At this point the pressure tester will automatically stop and tell the user it has failed the test.

In a wet test, The chamber is filled with air in a similar manner as the dry test. The watch is then lowered into a transparent tube containing water. The pressure is then released while the watch is suspended in the water. If nothing happens with the watch it passes. In the case of water intrusion, displacement will cause air to be forced out of the case from its weakest point. For diagnosis purposes, this is excellent for pinpointing exactly where the leak has occurred. Because there is a very real chance of the insides being damaged in case of a failure, this test is performed after it has passed a dry test or with the movement removed from the case solely for diagnosis purposes.

WATER RESISTANCE

WATER RESISTANCE

In all cases, hot water should be avoided. Even the worlds most water resistant dive watches have instructions to not take the watch into a shower, sauna, hot tub or other comparable conditions. The heat causes the seals to change shape and consistency in a way that can compromise seals. In addition to the heat, going from extreme heat to cold like when brushing your teeth after a shower, or sitting in the sun followed by jumping into a cold pool or lake can cause leakage. When the watch is hot, the seals get softer and the air in the watch expands. When the watch is exposed to cold, the seals and the air in the watch contract and water or even moisture in the air can be drawn into the watch.

WATER RESISTANCE• Watches generally have three main points that water can penetrate the case: The crystal, the case

back and the crown/tube/pushers.

• Gaskets, preferably from the manufacturer, of the correct size and shape should always be used.

• Gaskets and sealing components, whether new or used should always be thoroughly inspected. Just because it came out of a package doesn’t mean that its in the proper condition.

• All crowns and pushers need to be properly seated and screwed in where applicable.• Crowns and pushers should never be operated while

submerged. With the exception of a very select few watches, the seal will instantly be voided if the pushers are operated in the water.

• Any cracks or chips along the gasket of the crystal can allow water in. In this case the crystal would require replacement.

DIVE WATCHES

• Water resistance of at least 100M

• Luminous material on all hands and hour markers

• Visible second hand to indicate the watch is running

• All hands must be easily distinguishable.

• A uni-directional rotating bezel with the last 15 minutes graduated in one minute increments and a luminous orientation point at “0”.

• Watch must be shock resistant as well as chemical resistant and resistant to magnetic fields to a set tolerance.

• Quartz watches must have an end of life indicator.

Scuba diving watches fit into their own classification for water resistance under ISO 6425. The requirements are much stricter as these watches fit a particular set of needs to professional divers. Some of the criteria include:

HELIUM VALVES

For certain types of construction or research, divers may spend prolonged periods of time in a diving bell. This is referred to as saturation diving because the amount of time spent in a mixed gas environment causes the divers tissue to become saturated with the maximum amount of inert gas the bodies tissue can absorb. One of the gasses in the mixture that is breathed in this environment is helium. While helium itself is in no way harmful to the watch, it is able to penetrate even the most robustly constructed case because its particles are so small they can squeeze between the gaskets and the case. This helium gas will build up in the case as the diver spends time in the diving bell. When it comes time for the diver to leave and begin the decompression process, the pressure on the case is reduced and the gasses inside will expand. While the helium was able to slowly seep in over a long period of time it is now being forced out at a much more rapid pace. Without a clear escape route the pressure it will press on all the seals and usually result in the crystal blowing off.

HELIUM VALVES In the 60’s, when this kind of diving was starting to

become much more common, it became apparent that something would need to be done to protect dive watches from this phenomenon. Co-invented by Rolex and Doxa, the helium escape or helium release valve is a one way automatic valve that allows gas to exit the watch but not enter. It is spring loaded inward in a way that makes it so the pressure exerted from the outside actually pushes the valve in, reinforcing the seal, but when pressure builds up in the watch the valve will be forced out until the gas escapes and then it will go right back in without leaking.

Since the invention of the helium release valve, many companies have made their own designs. Many of them are not automatic and require the user to unscrew a valve to manually relieve pressure. While this device is becoming very common, very few people have a use for it so it is more often just a novelty. While rare, it is possible for the crystal to pop off when the pressure drops when taking off in an airplane and a helium release valve will protect against this as well.