Crystal polishing example

[jdm]

Beginners often ask about where to find this or that crystal, as it happens replacing is cheap and easy as long they are just flat round ones. But the crystal may not be found as generic, or can be expensive, or hard to find. So good old polishing is needed. Here again my technique key points:

• Crystal mounted on case, that will make it so much easier and safe to handle. Caseback removed, check below why.
• Jeweller's motor or other rotary tool with a fixed stand. You really want a screen like a carton box.
• Plastic roundel from a credit card as big as its size allows.
• 600 grit wet paper. No other grit is needed, as it will lose abrasiveness already after 20 seconds of use and become comparable to finer grades.
• Try to got directly over the deepest scratches, but without insisting too long (as in 5 seconds max) so to not dig valleys. Find the right compromise regarding the work angle, going flatly is good, but isn't even reasonable to try to sand the entire surface even.
• Look at the white streaks from inside the glass while working. You will see if you're getting right at the scratch or nick because if so the defect will show up in contrast
• Be patient with the paper stage. After a while it becomes hard to see if all scratches are gone, but you must remove them all before going to the next step.
• You should have made a mental note or drawing of where the defects are, rinse it up and observe at different angles. In difficult cases you may need to replace paper once or twice.
• Crystal will look now very foggy, that is normal
• Once happy refit caseback and crown, or rodico in the tube. The diamond paste is much more messy and you don't want that inside the case.
• Mount an hard felt wheel like 7 or even 10 cm dia, 2cm thick, place 1 cm of diamond paste (No. 10 or 14 good, but others work too) on the section toward you while keeping the crystal horizontal.
• Let the wheel grab the compound one bit a time, keep well pressed up and go over until all paste is used and you can present the entire surface to the wheel, rotate the watch and collect the past on the other side, place it on the crystal again on the other side. You can't do more than 30 - 40 seconds of work before adding fresh paste. Usually I do 4 or 5 passes like that.
• When working with paste is almost impossible to see the result with cleaning up. Clean with dishwasher detergent, dry it and observe well. Very likely you will notice some small defects, up to you if you want to go back to paper, concentrating on the spot only.
• Final polishing can be done switching to another wheel and finer paste, no less that 10 as these have no practical effect. Cerium oxide is another option but I didn't try it extensively so far.

Below what I did today in about 20 minutes. The central scratch was quite deep. No final polishing or cleaning yet.

After:

 

[jdrichard]

Great post. Thanks as I need to do this in a couple of weeks


Sent from my iPhone using Tapatalk Pro

[jdrichard]

Sent from my iPhone using Tapatalk Pro

[gary17]

Hey guys

Whats the best way of removing scratches from watch Mineral glass,acrylic and saphire? Do you use the same material for all?

Do you use sand papers?

can you do it with a dremmel? are there certain dremmel tools i need.

Is there a special paste you use?  cleaner? are there grades in the cleaner?

What are these scratch removing pastes i see?

What do i need to try removing scratches from the glass?

Dont want to buy a load of gear that ends up being useless. or even worse makes the glass unusable.

cheers

gary

 

[jdm]

10 minutes ago, gary17 said:

Whats the best way of removing scratches from watch Mineral glass,acrylic and saphire? Do you use the same material for all?

I've tried my best to explain above how's done.

[gary17]

Cheer JDM

Does that work for acrylic as well as mineral and saphire?

Were can you get the hard felt wheels?

gary

Edited January 6, 2022 by gary17

[jdm]

14 minutes ago, gary17 said:

Does that work for acrylic as well as mineral and saphire?

Acrylic is easily polished by hand with any compound on a cloth.
About sapphire, show me first a good picture of the problem and we'll go from there.

[VWatchie]

For acrylic crystals I remove them from the case and then use different grit wet paper, 600, 800, 1000, 2000 and finish it off with Polywatch. The result is always perfect. However, if you use this method be careful not to sandpaper the circumference of the crystal as it, naturally, will reduce its diameter. I made this sorry mistake on an original Omega crystal. Never again.

For mineral glasses I use "Glass (Mineral) Polywatch Repair Polish" which works really well for light to medium scratches. However, if I were a professional I'd probably want to use a rotary tool technique instead. I'd be interested to try the technique described in the 1st post in this thread. I get the overall idea but I unfortunately several of the points are unclear to me and I wouldn't expect the author to elaborate so I won't even ask.

Sapphire is probably near impossible to polish so I would recommend replacing.

 

[clockboy]

I have in the past removed scratches from watch crystals but for me the amount of time it takes I much prefer just to replace. For fine scuffs I did purchase this in two different grades which does work fine.

 

[jdm]

On 1/15/2022 at 1:22 PM, VWatchie said:

 I get the overall idea but I unfortunately several of the points are unclear to me and I wouldn't expect the author to elaborate so I won't even ask.

I'm "the author" and let me tell you that your assuming comment is plain wrong. I'm always willing to clarify on any point of my postings, to you or anyone else. So let me know what is unclear to you.

[TimpanogosSlim]

For "Mental note of where the damage is" you could use the method that machinists rely on and rub some dye into the defects. 

Officially that's Dykem Blue, in reality it's often a sharpie. You can get "heavy duty" sharpies that are more persistent (these work as etchant resist too!). You should not use a sharpie on acrylic / plastic because it has solvents that will allow it to soak into the material permanently. 

The middle road is laundry bluing applied with a brush maybe? 

[jdm]

7 hours ago, TimpanogosSlim said:

For "Mental note of where the damage is" you could use the method that machinists rely on and rub some dye into the defects. 

Not into the defect as in practice wet sandpaper eats it, but you can sharpie mark the other side. It may help but since you must not grind too small and localized, one can do easily without.