what year did they start using Plastic Pocket Watch Crystals?

Larry

Larry that is a real can of worms. Celluloid Plastic was actually in use before 1900. Molded plastic came into being in the 1920's. Then you have some other cellulose derivatives that could have been used even earlier.
One thing is for sure, the later very hydroscopic acrylic lenses ruined the hands over time because they were permanent "humidifiers".
So MANY TIMES a watch comes in with a perfect movement, an old yellowed out lense and sticks of rust for hands.

Thanks Dave nothing works worse than a pocket watch with a sickly green crystal, and the loss of hands that are hard to replace makes it even worse

sticks of rust for hands!!!!

lolololololol

I love that, I have a few too!

My advice is that if a crystal is yellow or green in color get rid of it ASAP

Bob

How can you tell the difference between a glass vs plastic crystal?
I tried the old, tapping with the finger nail trick but my hearing is terrible and I can't tell much difference.

Thanks
Ed

Generally the plastic crystals (left side picture) have a softer "roll" at the edge radius, while the Glass (Right side Picture) has a Bevel, or No "roll" at all.

Lindell tried to walk me through this today. I am still now to sure what I hear when I tap on it. Maybe this pic will help.

My personal favorite has always been tapping the crystal on a tooth ( a real one ,of course! ), the "ting" is almost always unmistakable.

If you really can't tell if the crystal is glass or plastic, take a pin and try and scratch a little bit of the crystal, in a place that won't be seen. If the pin leaves a scratch, the crystal is plastic, if not, it's glass.
Brian C.

this may sound odd but i tell by feel to me glass feels cooler to the touch then plastic.but then you have to play with a lot of crystals to get the feel.