I'm really not sure whether I have plastic or glass for crystals on my pocketwatches and wristwatches. How can one tell the difference?


Stephanie

Second question. What is the preferred crystal by most? I'm sure when having a crystal replaced, plastic would be cheaper right? I would personally prefer glass!

Stephanie

Glass is the only way to go. Plastic may be cheeper but you get what you pay for. As far as tinted crystals go they are junk. Most of the time it is an old plastic crystal deteroriating and this causes a green or yellow tint. Get them off your watch right away or soon you will have tinted hands also. Rust tinted that is. As the plastic rots it lets off a gas that will rust the hands in short order.
As far as being able to tell plastic from glass I use a sledge hammer if it shatters its glass and if not its plastic. And for the truth I touch it to my lip. Glass always feels colder and dosent adjust to temperature changes as fast. Also as long as its not a hunter crystal you can click it on your teeth. Thats how I do it anyway.

Aaron Bereiter


Looks like Jerry gave the same info on the WW section, oh well.

[This message was edited by Aaron on April 23, 2003 at 19:35.]

I'm in line with Aaron on this. If a watch is going into my personal collection, it will definately have a glass crystal. Even if I have to replace it with one. Plastic just tends to cheapen the whole watch. It is convenient and about 65% of the watches I buy to sell have plastic crystals. They are cheaper to replace.

In addition to the temperature variation between plastic and glass, you can try pressing VERY LIGHTLY on the center of the crystal. Glass won't give, plastic will. This is a little risky. You have to be careful or you will break a glass crystal, especially hunter. I will also take a pocket knife and lightly tap the center of the crystal. Glass has a faint ring to it where as plastic sounds dead. Takes a little practice to distinguish between them but it is distinct when you develop the ear for it.

I like glass crystals better also. However sometimes a plastic crystal is better. If someone carries a pocket
watch at work and is a construction worker, plastic may be better. Also, most dollar watches came with plastic crystals and should be replaced with plastic when changing the crystal.
Brian C.

One thing to keep in mind is that the use of plastic crystals has a long history. G&S starting making plastic watch crystals about 1900, so a pre WWII watch with a plastic crystal is not necessarity "wrong". The oldest of the plastic crystals tended to turn a "greenish" tint with age, those slightly newer went to a "yellowish" color. Modern examples will not turn color and do not promote rust on the hands and cannon pinions as the older ones did, as they are made from a different material.
Replacing old crystals that have started to change color is a good idea, as it may prevent corrosion problems later, but the choice to go with glass or plastic is a matter of personal choice and the conditions under which the watch will be worn.

Ed Ueberall
NAWCC #49688
IHC #34

Aaron,
I chuckled - sledge hammer to detect whether glasss/or crystal Ha!
I'll try the lip test you recommended. I only have one colored crystal (blue) on a wristwatch. It will stay.

Doc -
Your glass/plastic test does sound risky. I'll stick with Aaron's lip test. Poor lips

Brian C,
A construction worker should wear a hunter watch!

Ed - the Railroad Watch Expert
Thank you for your information! I'll watch out for those "greenish" and "yellowish" crystals in the future!

Looks like glass rules thus far!!


Stephanie O'Neil
NAWCC#0143979

Stephanie.
I use cerrium oxide to polish crystals. I got it from a local guy who does stained glass. It works great and readily removes light scratches and scuffs.
Toothpaste works well also but is not nearly as effective. Try one of those whitining types as it has a light abrasive for your teeth. And as an added bonus if you ever sell it on ebay it really will be "minty". No fibbin.

Aaron Bereiter

Hi Stephanie,

A member on one of the other boards claims he tells the difference between glass and plastic by licking the crystal.

Of course, I wouldn't recommend this method while viewing watches at a mart or flea market.

I definitely prefer glass but my focus is primarily on pockets that predate plastic crystals by quite a few years so glass is appropriate. Whenever I see a description of a watch circa 1870's - 1880's as having a new plastic crystal, it makes me cringe.

Jack

Yikes! I sure agree with Jack about keeping your tongue "reeled in" at watch shows far a variety of reasons! Some say they can "taste" gold versus gold-filled too. Well not on my watch!

Ed's observations as always are well-taken. Some early plastic crystals in the 1920s and 30s did a lot of serious damage. They turned yellow and even a sick green. If you find one that has "turned" get it out of there today! The later plastics were no problem.

You'll find most older RR grade pocket watches were required by the rules to have a glass crystal in order to be absolutely clear. Then at the time of WWII the US Government specified an unbreakable crystal for obvious reasons on their orders.

After the war plastic and lucite became the preferred crystal among many RR men, but most collectors today want a slightly beveled glass crystal.

Many wristwatches use only plastic, even very good ones. I also find some gold cased pocketwatches are better with plastic as the gold bezel will flex too easily and pop out the hard glass crystal. I also find on a lot of hunters the glass crystal is so thin that plastic is preferred in order to avoid breakage.

Fitting a watch with the kind of crystal it originally would have of or at least could have come with is always a wise move.

Lindell

I should probably clarify my comments above as I may have been focusing too much on my own collection while commenting. Like Jack, nearly all the watches that I collect pre date plastic crystals. Originality is definately important. I wouldn't promote placing a glass crystal on a watch that originated with a plastic one.

Certainly, watches that will be worn would cause much less headaches if they had a plastic crystal.

I still hate to open the lid of a hunter and tap the crystal only to hear that thunk sound that plastic makes.

While on this subject let me pose another question. Does plastic still fall under the description of "crystal"? I am of the mind set that it does but have been scolded in the past for calling plastic a crystal in my auctions. What do you say?

BTW, if you are not fond of french kissing a watch at a mart, you can always feel the difference in temperature by holding the crystal against your cheek. It's just not as sexy!

Boys, I'm back.

Aaron,
I'll write it down "cerrium oxide" -to readily remove light scratches and scuffs. May try the toothpaste!

Jack,
"Licking the crystal?" How funny!
My tongue is long but we won't go there! Ha!
How sanitary can that be anyway?
I know what you mean about putting new pieces(such as a new plastic crystal) on a circa 1870 piece. I'm a purist when it comes to that stuff.

Lindell,
Tasting gold vs. gold filled? That's interesting!
I'll keep the valued information handy.

Doc,
A good question indeed - "Does plastic still fall under the description of crystal? Sometime back I needed a crystal on a pocketwatch. A plastic crystal was put on and I was surprised. Honestly, only yesterday did I realize by reading people's responses on this site that crystal denotes either glass or plastic. Frankly, I always thought crystal was glass, not plastic.

Stephanie

To to add to the "is plastic a crystal?" discussion, many newer high grade wristwatches use sapphire "crystals" which are neither glass nor plastic.

Ed Ueberall
NAWCC #49688
IHC #34

To add something to a 10 year old thread....

Strictly speaking neither glass nor plastic is a crystalline substance. Glass is a supercooled liquid. If it does crystallize it becomes a ceramic of some kind and no longer transparent.
Now sapphire is a crystalline substance.

But in the case of a watch, it is a crystal if you look through it to read the time, no matter what it is made of.

Tom,
To further pile onto a 10 year thread, you're mostly right: glass is amorphous "liquid-like", but its cousin quartz is crystalline and can be quite transparent.

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Evan

If you ever look at an old window pane you will see that it is thicker at the bottom than at the top because glass never attains a crystalline structure.

Francesco,
That's a common, but incorrect, myth according to my materials science professor in college. Old glass is thicker at the bottom because of how it was made--it was positioned vertically before it was completely cooled, thus making the bottom fatter, with visual sags.

Evan

That may explain regualr windows. But not stained glass ones. During WWII many windows were taken out across Europe to protect them. When some of the pieces were taken out to repair the window the same bottom heavy than the top was found when the pieces were weighed. The top and bottom of a piece of stained glass is not necessarily the way it came out and hanged to cool. As craftsmen try to get the most number of pieces from a sheet the patterns of the pieces are turned to maximize the use.

I always want lass crystals on my collection watches. However modern acrylic, plastic or whatever they call them are a good choice for watches carried for regular use. I carry mine in a pocket and may inadvertently put stuff in my pocket that damages or breaks glass so plastic on a daily user is fine with me. As many have noted the older plastic crystals gave off a corrosive gas that destroyed hands and they should always be removed. When in doubt get rid of it. I finished up a cerium oxide polish on an older heavy 18s Hampden crystal and it came out nice. Has anyone used the windshield chip repair stuff on a crystal?

I totally agree with Deacon's position on this and must add that if you are lucky enough to have a supply of plastic "Hunter" crystals you are "ahead of the curve" using them to restore Hunter Cases.

As for "Cold Flow" of Glass the math does not stand up. Some Wickipedia factoids on that subject;

Writing in the American Journal of Physics, materials engineer Edgar D. Zanotto states "...the predicted relaxation time for GeO2 (Germanium Dioxide) at room temperature is 10-32nd Power years. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer." (10-32nd power years is many times longer than the estimated age of the Universe.)

If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more — but this is not observed.

Similarly, prehistoric obsidian blades should have lost their edge; this is not observed either (although obsidian may have a different viscosity from window glass).

If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then the effect should be noticeable in antique telescopes. Any slight deformation in the antique telescopic lenses would lead to a dramatic decrease in optical performance, a phenomenon that is not observed.

There are many examples of centuries-old glass shelving which has not bent, even though it is under much higher stress from gravitational loads than vertical window glass.

Further, Cathedral Glass was actually blown (as were early watch crystal glass) and the glass cutting was always done to place the thicker side down so there was a better weatherseal to the lead "I" shaped supporter.

Since Mr White is on a crystal making sabatical, I have tried to find a source for the plastic crystal, about two years ago I had found a place but sadly when my pc crashed that link went with it. I prefer glass but would agree for hunters that plastic is probably better since glass hunter crystals are so fragile, the sometimes I think they break when you look at them.

David,
You're a gentleman and a scholar. You weren't sitting next to me in that class when I nodded off were you?

Evan