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Discussion Starter #1
This is something that once in a while, comes up on WUS and answers are typically given.
However, as good as simple descriptions can be, nothing beats a good step by step guide.

As some of you might know, I build scale model kits of cars in my spare time, things like these:




Part of that process involves a rather painstaking sanding, polishing and finishing on the paint for the bodywork and it is that exact same process that can be applied to acrylic crystals and even metals such as the stainless steel on used on watches.
The harder the material, the more work you have to put in but the process remains the same.

Polishing any material is essentially a process where you remove material to the depth of the scratch you want to remove.
Thus, if you are only removing hairline scratches then you can probably give it a once over with a fine finishing paste of some sort and be done.
If however, it is a deeper scratch, then you will need to sand down the surface until the scratch is no longer there, before finishing.

The question is then about how much finishing you need to do. After all, if you've just taken out a 1/5mm scratch, then that means you've used pretty low grit paper on it (or spent a long time using a high grit one...)

There is actually a "correct" method to this that 1:1 automotive guys follow in which each next step of sanding, is twice the grit of the previous.
If you started with 600 grit, you move up to 1200, then 2400, then 4800 (or similar) and so on.


I buy a lot of older watches, some of which some with acrylic crystals. Inevitably, not all of these are going to be anywhere near perfect and even ones that look good at a distance can actually be full of scratches on the surface. Armed with my modelling experience, polishing out the crystal is often the first thing I do to freshen up a watch, if anything, to give me a better look at the dial.

So how do I polish acrylic crystals?


To be continued.....
 

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Discussion Starter #2
...continued...


ok, I posted some quick photos of my latest 1020 elsewhere but here it is again.



you can't really see the state of the crystal but it is quite scratched.
you can see some of the surface damage in this closer cropped shot.



So, what can I do about it?
First of all, these is what I'll be using:


I've labelled the grit of the various papers and pads I typically use.
You should find most papers up to 2000 at good automotive supplies stores. The 4000 and 6000 are Micromesh (brand) polishing cloths and the Tamiya compounds are both found in good modelling supplies stores. If you're just taking out hairline scratches, just using the blue cap (Coarse) compound is usually enough to do the trick.
The blue rag is what I use to apply the compounds.

But this watch requires more work.
For those that have never done this before, this can be quite scary because you are going to be literally taking sand-paper to your watch crystal.


sequence to follow.....
 

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time for some sanding....

there are some deep scratches on this one so I will start with the 600 grit.
What you have to do, is to give a good even "grind" as it were to the surface of the crystal. What you want to avoid, is an uneven surface as this will have an effect on the clarity of the finished result. An uneven surface will result in distorted reflections and views through the crystal.


Step 1: 600 Grit.
I sand with a little dab of water on the paper to help carry away the excess material - most of time, I actually just give the paper a little lick and that is enough moisture to do the job.
After a few passes, you should end up with this.


Yikes! the whole surface is now scuffed up to the point that you can see through it!
Relax, this is what we are after. What you are doing here, is sanding down until the deep scratches are gone. Material has been removed to the depth of the scratch and as a result, the surface will be all scuffed up.

What I do, is to carry out a series of passes in each of the cardinal directions, then along the diagonals as shown by the arrows here:


This is to ensure even sanding.
For each stage of sanding, I follow the same pattern/directions.

Subsequent sanding is now done to gradually reduce the size of the scratches that form the scuffed surface until they are virtually all gone and/or taken out by polishing compound.

Step 2: 1200 grit.
After the passes, this is what it now looks like.


As you can see, it is just a little bit clearer than before.
This is what happens as you move up each Grit; it will get clearer and clearer.

2000Grit


4000 Grit:



6000 Grit:


You can see that by 4000, the crystal is already much clearer than before and typically, 4000 is where it happens with clear acrylic. Some of the clarity is due to moisture/lubricant in the shallow scratches that give the impression of a perfect surface.
In reality, there is however, still a layer of very fine matting on the surface which the finishing compounds will take care of.


Coarse Compound:


and the final
Finish Compound


In that final photo, what you'll notice is that reflection of the overhead lamp is now a very crisp image and a very definite clear reflection, even if you compare it to the previous Coarse Compound photo.


Now please bear in mind that I only did a quick job on that one to freshen it up a bit and it isn't a complete scratch removal. In fact, you can see the time it took as I was taking photos of it on the fly so the snaps are "real-time".

After taking care of those smaller scratches, I can now see that there are deeper ones that will take more work to get out. In addition, there is some age/stress cracking on the lower right hand corner that I couldn't see before because of those other scratches. It looks likely that I'd be wanting to get a new crystal for this one after all...



As I said before, this process is the same for any material.
For example, I turned this bezel and edging:


into this


using pretty much the same materials but with a lot more elbow grease.



Hopefully, that takes out some of the mystery of polishing for those with scratched acrylic crystals.
 

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Discussion Starter #5
...and to finish...


a couple of comparision shots.

before:



after:




and I couldn't see before under the scratches but the Omega logo is on this crystal marking it as an original part.




I only wish I did this during the day so my camera would've taken better quality photos in daylight.
 

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Thanks for the tutorial, and great pictures! You're right, I would be pretty nervous after that first round with the low-grit sandpaper.

For shallow scratches, it's probably easier to spend 5 minutes with some polywatch, which works very well (https://www.watchuseek.com/f2/adventures-polywatch-899434.html).

Your method is probably better at removing deep scratches or dings though, just requires more effort.
 
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Thanks for sharing DM. Only one problem though - if one of my babies wins a scratch it looks like a trip to London is on the cards. :-d
 

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Discussion Starter #11
At the top of this, I said that the same process is done to pretty much any/all materials from which you wish to remove scratches from.
On a watch, this is typically going to be stainless steel.

First of all, I shall open with this:
This isn't how a watch-maker would do it.
What they would/should do, is disassemble the watch case into its constituent parts
i.e barrel, bezel, caseback
and then refinish the surfaces as necessary on a variable speed polishing/buffing wheel.

Well I don't have any of that.
What I have, is my stash of sanding papers and a lot of masking tape.

Let's get to it!

Step 1: Masking

The target of this exercise is that polished bezel. It's had a pretty rough life before the watch got to me and is a little dinged up. Some of them are quite deep and I won't be able to get them out without removing too much material for my liking. What I can do though, is to smooth them out a bit and make them less noticeable.

First of all, I need to protect everything in the area that I don't want sanded
(yes, I probably should've done this before the crystal)

I start at one corner and work my way around, laying new strips on top of previous ones to aid removal later.


until I get this:



next comes making up the crystal:



then it's back to my friends the sanding crew.
I have to admit that I actually had a go at this last night while my fingers were still a little itchy after polishing the crystal so the bezel has already been through one round of this process.
You can see here that the bezel is already flatter and more free from hairline scratches but it isn't polished and still a couple of deeper marks visible


instead of 600, I started straight with 2000 this time.
The reason I used 2000 is because the scratches aren't that deep so I don't need that harsh a grit to work them out. However, because steel is much harder than acrylic, you have to be a little more forceful when sanding it. What I also do, is instead of a little water/spit, I use a little of that Finish Compound to act as a lubricant.
This is what I get after using the 2000 Grit:


You can still see the marks on the bezel but more importantly, you can see some black gunk building up. This is actually the steel being reomved and mixing up with the compound.

different angle


Not glossy yet.


I continue with the 4000 Micromesh pad and it starts to shine up.
As before, I use a little Finish Compound to help.


moving onto 6000 and the reflection starts to gain clarity



From this point on, it is just a case of continuing to polish the bezel with the 6000 Micromesh pad with Finish Compound. If you like, now is the time to break out the Dremel, which I did.
I added a little Finish Compound to a polishing pad, cranked it up to about 1/3 power and worked on the bezel. Note you have to press down quite hard. You are still wanting to remove material using the Fine Compound to take out those teeniest little hair scratches.

After a couple of minutes, remove masking tape, give the watch a wipe down to remove stray polishing materials and viola!


compared to yesterday



Hopefully you can see the difference in the clarity of the crystal and the reflection on the bezel.


It's not a perfect finish as there are some deep scratches that will need a lot of work that you can see here.




before:


after




and to finish, a little quick shot in a setting.


and a close up crop


It's not perfect but it's better than before.
 

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Discussion Starter #13
thank you.
it gets a bit addictive.

I gave it another two rounds on the bezel since those photos and this is what it looks like today.
(photos taken not in direct light so you can see the clarity of the polish)



I think one more go might be on the cards and then I will definitely try and get a final daylight shot.


It's a little hard to get a good shot of the bezel as it is really only 3mm wide and trying to focus on the reflection in that is difficult. In real life, it's much easier to see the results my polishing achieves.
 

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That is outstanding and a great tutorial. Can I ask you a question, does the paste compound have a solvent base? The reason I ask is that I've used polishing compounds on bikes and brasso on watch crystals and I have an allergy to the solvents. Don't know about polywatch either come to think of it. Do you think a watchmaker would polish a crystal for you for a reasonable price?

I have a Timex electronic on its way that has a crystal that looks like a frosted car windscreen.

Great watch BTW, lucky you.
 

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Discussion Starter #15 (Edited)
That is outstanding and a great tutorial. Can I ask you a question, does the paste compound have a solvent base? The reason I ask is that I've used polishing compounds on bikes and brasso on watch crystals and I have an allergy to the solvents. Don't know about polywatch either come to think of it. Do you think a watchmaker would polish a crystal for you for a reasonable price?

I have a Timex electronic on its way that has a crystal that looks like a frosted car windscreen.

Great watch BTW, lucky you.
The polishing compounds do not have a solvent base.
For clarity; those compounds are originally meant for use over modelling acrylic paint and so are very un-reactive or else it would affect the paint in a bad way.

I haven't used Polywatch but I'll assume that it is the same. I should point out that I haven't used Polywatch because I already have experience using the Tamiya polishing compounds on paint, plastic and metal, not that I have anything against Polywatch itself.
The difference between this sort of polishing material and stuff like Brasso, is that Brasso is a metal polish which has a chemical/solvent element in it that is for removing tarnish. In what I use, it really is a medium in which particles are suspended which is the abrasive material doing the work. Unlike the chemical tarnish removing chemicals, it also doesn't react with the occasional bit of paint you might find on a watch
i.e painted bezel numerals/markers.
 

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This is going to be heresy to some, and I may wind up getting run out of town on a rail for admitting this but...

I have a Marathon Navigator that wears a Hesalite crystal, and, as Hesalite is wont to do, it acquired an assortment of scratches in short order when I started wearing it. Most of the scratches were fairly superficial, but a couple were decently deep. After pondering the matter for a bit I wound up putting a small dab of toothpaste on a kleenex and buffing the crystal lightly. It took me maybe 2 minutes to remove all the scratches, even the deep ones. The only downside was that the watch smelled like toothpaste for a while. But at least it didn't have any cavities.

I'm quite certain the ease of doing this, and the success of the operation, were both down to Hesalite being such a soft material. I very much doubt this strategy would work on mineral crystal, let alone sapphire.

Just one more data point in this discussion. (And a reminder to me to see about getting that Hesalite abortion replaced with something more durable.)
 

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Some of the model builders use toothpaste on clear acrylic too so you wouldn't be the only one.

The thing is, the "grit" in toothpaste is not necessarily uniform, nor is it necessarily of the required size.

I follow the polishing paint method so I'm comfortable confident in using the various stage grits for this sort of thing. Most people here are likely to only ever need Polywatch or in your case, toothpaste. As I said when I started at the top, I was taking out more than a few hairline scratches so I needed to use a harsher abrasive to start with then work my way up the grits.

If I was just dealing with minor surface scratches I could probably have just done with the last two stages
I.e 6000+compound
 

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Thanks DM; I have polished crystals and bezels in the past with hit or miss results. Ever since I saw some very polished pullys from leather belts on old power train for sawing lumber, plus how leather is used to strop razor blades, I made up a bunch of narrow wooden blocks with old leather from discarded belts; the leather is stapled to the wooden blocks to give a narrow but flat surface to use in polishing surfaces like bezels and crystals. I use various grits of dry compounds to 'charge' the leather. Pumice powder with a drop of water works well. Jewellers rouge also helps in polishing. My technique is not as fast as yours, but I am too afraid of taking away sharp details on bezels, etc.

Your tutorial will help me achieve faster results.

John
 
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