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Hi,

I have tried to polish the scratches out of my pocketwatch plastic crystal, but it has instead gone really sticky and cloudy. Its like it melted the top layer of plastic. Maybe this happened because the plastic is yellowed and old? The sticky residue is a bit like the glue left behind when removing a sticker.

Steve

20230514_191213.jpg

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19 minutes ago, stevemilw said:

Hi,

I have tried to polish the scratches out of my pocketwatch plastic crystal, but it has instead gone really sticky and cloudy. Its like it melted the top layer of plastic. Maybe this happened because the plastic is yellowed and old? The sticky residue is a bit like the glue left behind when removing a sticker.

Steve

20230514_191213.jpg

What did you use to polish it Steve

21 minutes ago, stevemilw said:

Hi,

I have tried to polish the scratches out of my pocketwatch plastic crystal, but it has instead gone really sticky and cloudy. Its like it melted the top layer of plastic. Maybe this happened because the plastic is yellowed and old? The sticky residue is a bit like the glue left behind when removing a sticker.

Steve

20230514_191213.jpg

Before acrylic crystals, cellulose was used. Aged cellulose is likely to be more reactive than acrylic. 

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9 minutes ago, LittleWatchShop said:

IPA reacts with acrylic

It's quite possible that the problem is that your crystal isn't acrylic at all, but rather celluloid.

Celluloid was the early "unbreakable" alternative to glass for watch crystals long before we had acrylic and one of the problems that you get with celluloid is that it discolours with age, typically yellowing. You can't polish it out either as it is all the way through.

I suspect that there is something in the Polywatch that dissolves celluloid, it ought to be absolutely fine with acrylic since that is specifically what it is made for polishing.

One of the other undesirable qualities of celluloid is that it degasses, the products of which can accelerate rusting of steel.

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10 minutes ago, Marc said:

It's quite possible that the problem is that your crystal isn't acrylic at all, but rather celluloid.

I've got to concur with @MarcIt is more than likely a cellulose compound the crystal is made from. If it had a yellow sheen to it and had some serious age to it, then it's very probable.  There is nothing you can do to resurrect this one, I'm afraid. Always best to replace one, as you can't even see through some of the really bad ones , unless it isn't too bad then you might want to keep the originality of the timepiece. Some will have their views on patina of dials and hands, etc. Personally, I like to see some history that has been etched into the watch case; not necessarily the acrylic though. I do like to give an original acrylic a polish to remove the major scratches by starting off with some 1200 grit wet and dry, or powder charged on a cotton bud, then go through various grit counts to end up using something like cerium oxide as a finish. I find original acrylic crystals, say from the 60's or 70's have a nicer smoother rounder profile than the modern day ones which are a bit blocky in my opinion.

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One of the more "interesting" properties of some older clear plastic objects (and this includes old film stock, and some old watch crystals) is that they are made from nitrocellulose.
Of course this makes them interesting in a similar way to the way that radium dials are interesting. They have a certain level of mild peril associated with them.

Nitrocellulose is the main component of old fashioned "gun cotton" explosive.

Nitrocellulose film stock for this reason is notorious for spontaneous combustion, and furthermore for being almost impossible to extinguish, since it contains its own oxidizer. The reason more recent types of film stock are called 'safety film' is because they don't have this rather inconvenient property.

With this in mind, and if you are up for a small and mildly hazardous experiment, you might want to replace the yellowed crystal with a modern alternative, and then try burning the old one. If it burns rapidly and rather alarmingly, then it is made from nitrocellulose. If it melts and burns rather poorly, then it is a more modern acetate based crystal.

The usual caveats apply, you obviously do this entirely at your own risk. Don't forget to film the results. Burning down your entire neighbourhood may well net you a viral video. You can thank me afterwards. 😋 

Edited by AndyHull
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Below is a link discussing in great details the issues with polywatch and older cellulose crystals together with several methods to clean them and other types of crystal. Unfortunately I think it is too late for your crystal, but at least you will know for next time 🙂

 

 

As an aside I use Autosol acrylic paste, which I have found to work just as well as polywatch (I think its pretty much the same stuff - just in a bigger cheaper tube):

 

Acrylic_Polish__07093-2.jpg

Edited by Waggy
typo
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  • 2 weeks later...
On 5/14/2023 at 8:20 PM, Jon said:

I've got to concur with @MarcIt is more than likely a cellulose compound the crystal is made from. If it had a yellow sheen to it and had some serious age to it, then it's very probable.  There is nothing you can do to resurrect this one, I'm afraid. Always best to replace one, as you can't even see through some of the really bad ones , unless it isn't too bad then you might want to keep the originality of the timepiece. Some will have their views on patina of dials and hands, etc. Personally, I like to see some history that has been etched into the watch case; not necessarily the acrylic though. I do like to give an original acrylic a polish to remove the major scratches by starting off with some 1200 grit wet and dry, or powder charged on a cotton bud, then go through various grit counts to end up using something like cerium oxide as a finish. I find original acrylic crystals, say from the 60's or 70's have a nicer smoother rounder profile than the modern day ones which are a bit blocky in my opinion.

This is probably why then, thanks for clarifying. It felt like acrylic so i just assumed it was. 
I used Polywatch to polish it.  I'll get a replacement acrylic. 

On 5/14/2023 at 11:14 PM, AndyHull said:

One of the more "interesting" properties of some older clear plastic objects (and this includes old film stock, and some old watch crystals) is that they are made from nitrocellulose.
Of course this makes them interesting in a similar way to the way that radium dials are interesting. They have a certain level of mild peril associated with them.

Nitrocellulose is the main component of old fashioned "gun cotton" explosive.

Nitrocellulose film stock for this reason is notorious for spontaneous combustion, and furthermore for being almost impossible to extinguish, since it contains its own oxidizer. The reason more recent types of film stock are called 'safety film' is because they don't have this rather inconvenient property.

With this in mind, and if you are up for a small and mildly hazardous experiment, you might want to replace the yellowed crystal with a modern alternative, and then try burning the old one. If it burns rapidly and rather alarmingly, then it is made from nitrocellulose. If it melts and burns rather poorly, then it is a more modern acetate based crystal.

The usual caveats apply, you obviously do this entirely at your own risk. Don't forget to film the results. Burning down your entire neighbourhood may well net you a viral video. You can thank me afterwards. 😋 

Haha, very interesting. I might just try with a lighter and see what happens 😂

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3 hours ago, stevemilw said:

I might just try with a lighter and see what happens

You'll need to post the photos/video or it didn't happen! 😋

On the subject of polishing cellulose crystals, I have used T-Cut car polish with reasonable success. It wont however remove yellowing from such crystals, as this is not just a surface phenomenon. Not all crystals can be saved.

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