Watch crystal cracks

[Norken]

Hi! 

I’m new to amateur watch repair and refurbish and am very glad to have found this forum! 

Recently I have had issues with watch crystals cracking when I polish them. I remove the crystal from the case and start polishing with wet sanding sheet (grit 1000 & grit 3000) and water (with a dash of washing liquid). The polish have resulted in a cracked glass in my two last attempts. I guess some kind of tension have been built up but how? And more important, how can I avoid it? 

Thanks a lot!

 

[chrisdt]

Is it glass or plastic? From your picture it looks very scratched to be glass. Over time plastic becomes brittle and stars to degrade. The way forward then is a new crystal. At not very much money it can enhance the look of an otherwise dull and uninteresting watch. If its glass I have had some success with a small jewelery buffing wheel and a small amount of 'Dialux buffing paste. Place the glass on a soft surface and gently buff the whole surface. You can do it by hand but its a lot more work. Don't introduce too much pressure though because the heat generated will crack the glass. My own personal opinion for what its worth is 'New every time'

[Norken]

19 minutes ago, chrisdt said:

Is it glass or plastic? From your picture it looks very scratched to be glass. Over time plastic becomes brittle and stars to degrade. The way forward then is a new crystal. At not very much money it can enhance the look of an otherwise dull and uninteresting watch. If its glass I have had some success with a small jewelery buffing wheel and a small amount of 'Dialux buffing paste. Place the glass on a soft surface and gently buff the whole surface. You can do it by hand but its a lot more work. Don't introduce too much pressure though because the heat generated will crack the glass. My own personal opinion for what its worth is 'New every time'

It’s plastic, the scratches comes from that I had started the process to polish it. Agree that sometimes a new crystal is to prefer but quite often one can polish up the old one. But what could be the reason for them to crack like this did? Thanks!

[chrisdt]

As mentioned previously the plastic has probably degraded. It could have been cracked before you removed it from the watch. Sometimes cracks in acrylic are difficult to detect especially if viewed straight down. Sometimes only visible when looking at the rim.

Probably it was quite happy whilst in the watch but could not withstand the stress of being pushed out and polished. The rim is the weakest point.      

 

[Norken]

12 minutes ago, chrisdt said:

As mentioned previously the plastic has probably degraded. It could have been cracked before you removed it from the watch. Sometimes cracks in acrylic are difficult to detect especially if viewed straight down. Sometimes only visible when looking at the rim.

Probably it was quite happy whilst in the watch but could not withstand the stress of being pushed out and polished. The rim is the weakest point.      

 

Ahh i see. Could very well be the case then. You learn something new every day  will look more carefully in the future. Thanks!

[yankeedog]

I don't usually remove them. I think compressing old brittle plastic is bad mojo. I polish them in place, mother's mag and aluminum polish. put some on a paper towel , laid down on a flat surface. press down with light pressure  and do figure eights.

[oldhippy]

 I can never understand why one spends so much time in trying to polish, if the mark is not very deep there are many componds to use, but if the marks are deep buy a new crystal.

[VWatchie]

I use this method with my plastic crystals with fantastic results! I've never shared the experience of it cracking. I think you were likely just "unlucky" with this one.