Polishing Acrylic Crystals
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  1. #1
    Member drunken monkey's Avatar
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    Polishing Acrylic Crystals

    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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  2. #2
    Member drunken monkey's Avatar
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    Re: Polishing Acrylic Crystals

    ...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.....
    V.I.T., samanator, DM71 and 2 others like this.


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  3. #3
    Member novedl's Avatar
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    Glued to my iPad for the next installment....
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  5. #4
    Member drunken monkey's Avatar
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    Re: Polishing Acrylic Crystals

    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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    DM's Ghetto Watch Polishing Guide

  6. #5
    Member drunken monkey's Avatar
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    Re: Polishing Acrylic Crystals

    ...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.


    Thoughts for the day:
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    DM's Ghetto Watch Polishing Guide

  7. #6
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    Re: Polishing Acrylic Crystals

    This is certainly a very useful and welcome post. Thank you.

  8. #7
    Member novedl's Avatar
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    Great tutorial D_M_. Thanks for sharing your knowledge.
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  9. #8
    Member shameless's Avatar
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    Re: Polishing Acrylic Crystals

    excellent and informative post that im sure many to shy to ask will appreciate

  10. #9
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    Re: Polishing Acrylic Crystals

    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://forums.watchuseek.com/f2/adve...ch-899434.html).

    Your method is probably better at removing deep scratches or dings though, just requires more effort.
    rfortson likes this.
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  11. #10
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    Re: Polishing Acrylic Crystals

    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.

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