remove scratches from glass...another one :-)

[Kasper]

hi,

i know that the most of you don't care about getting the best out of a watch..most collecters only collect, so they buy nos.
But that's not my style...there are so many nice watches out there that only need a nice polishing, cleaning etc...the only thing i still haven't find a solution is polishing the glass itself. It's the next part in my learning curve I tried doing some with my dremel but it's not a good solution.

so within 2 weeks i will buy this sander and start experimenting.
Is there anyone who has experience in this sander?

http://www.proxxon.com/eng/html/28060.php

i allready have special polishing paste...and i now need to find the disk with between 1600 and 25000 (diamond)grade sanding paper.

http://www.benl.ebay.be/itm/3M-Wet-and- ... 84b92cb53f

this looks interesting.

so i need every bit of info and how you did it from you all.

[quietman]

I know you can buy many types of pastes, papers and other wizardry for this. Like you I enjoy refreshing beaten-up old watches and try not to spend too much on equipment so -

For 'rough' finishing I use the same as what I use for polishing steel - 800 grit -> 1200 grit -> 2500 grit wet and dry (carbide) paper. Easily available although I have to go to Halfords (a car parts superstore) for the 2500 grit. Only use it wet on glass. I have a polished granite surface which I 'stick' the paper to and the rub the glass - keeps everything flat and avoids rounding the perimeter edges which is not cool. Then I finish with 3 micron cerium oxide (cheap little bag off Amazon.co.uk). The cerium needs to be in a paste or slurry to work. I have a cloth wheel for my not-Dremmel which seems to hold up better than the felt ones. I have soaked this in a wet slurry of cerium oxide to 'infuse' it with a particulated pinkness. Then I apply a paste to the surface and slowly polish it. Low speed - long-time is better for this - and stop for a while if it gets too hot. I can't fill the case with water because I don't do it upside down but you could if you have a bench mounted wheel. I just hold the case with my thumb on the backside of the glass under where I'm polishing as an over-temp sensor.

When your watch glass is wet you obviously cannot see the pregress of scratch removal. I find coffee filters are handy for quickly drying the face to inspect progress.

Whatever you use be scrupulously clean and segregate all of your grits and powders or you risk wasting a lot of time with mysterious scratches appearing during final polishing. Clean off the glass well before moving down a grit size. Keep any 'infused' wheels cleanly stored for reuse only with that grit size. If your chosen paper has any folds, tears or areas of wear in the area you are using then use it for something else and get a new piece - one piece of detached grit will quickly spoil your day unlike it will on steel.

This method works well on 'older' mineral glasses although I must say it took a very very long time on my modern Citizen which (not sapphire) has some kind of unholy Mineral glass that will take a scratch quite happily from little knocks on everyday items but apparently doesn't very much like being re-polished.

Rgds,

MP.

[Derek]

Excellent "How To" post quietman

I'm tempted to try this on my Seiko A259-5010, but I don't know how to separate the glass from the case. I'm guessing it pushes out from the inside, but it seems to be quite firmly attached, so I chickened out in the end.

Is there a trick to getting the glass out, or should I just use brute force?

[quietman]

The only time I take the glass out of a case is if its broken and I want to replace it. Removing the glass from a case without the correct tools and dies will most likely lead to breakage either on the way out or the refitting. Plus you'll probably damage the gasket/seal. You can easily polish it up with it still in the case.......

You could a look at other polishing products too. My method is the 'cheapo' way of doing it. Some of the diamond papers such as those referenced by Kasper in his post are quicker than carbide but they cost a bit more

Lastly, whatever you're trying out for the first time I would really, really, really recommend practicing on a few pieces of junk before attacking something you actually like. I have bags and bags of cr**py old mechanical watches that I ruined in the pursuit of competence. And I still have a couple of really nice old mechanicals that I just know I'm not good enough to touch yet - perhaps a few more years and a few more bags of carnage.....

You can pick up a junk glass fronted watch or two from Ebay for the price of a few sheets of carbide paper. I'm not saying spend all day on it but it just gives you something to get the feel/touch of it all on and to develop a workflow that doesn't lead to a wrecked Seiko!

One thing you do need to be careful of when doing this kind of thing is the paint/printing/legends on the backside of the glass. Some are really tough but some of them really don't like water or excessive touching. Just take a little care back there.

And Good Luck!

[retroleds]

Kasper - don't buy that sander, you will be greatly disappointed. You can find small lapidary units in the $300-400 range. Then you will have water for cooling, and will easily be able to use diamond impregnated film or aluminum laps(discs), which are sold in ranges exceeding 3000 grit fineness. Inland company makes a nice tabletop lapidary unit for around $350 - I use/own one.

Cerium oxide use: someone mentioned making a paste, that is an incorrect use of that product. Cerium works both chemically and abrasively. Using a too heavy concentration in the water is self-defeating, as it cannot interact the same with the silicon in the glass. It generally takes a small amount of cerium slurry, maybe 1/2 tsp. in 1/2 liter of water, often desribed as "thick as watery milk". Put on a felt or leather pad and let it soak in and dry. Then wet it and keep it wet, only adding more cerium in small amounts. If you get tired of polishing, that is an excellent time to float a little more cerium juice onto the pad and allow all to dry into it. Rather than while polishing, which throws most of it off due to centrifugal force.My $0.02

Tin oxide works much better on some particularly grainy mineral glasses. Tin oxide particles are softer than cerium, and the Cerium unfortunately "micro-chips" the tips of the glass crystals, as opposed to the tin oxide which more gently shaves or rubs those sharp edges off the glass crystals/grains. Tin oxide is the ticket for your vintage Seikos...ask LEDluvr to post a picture of the one I did for him.

Diamond lapping film - much better than sandpaper. Sandpapers have many grains that are larger than what they are classified as, particularly cheaper papers. And the grains easily become dislodged, creating fresh scratches. Diamond film is made by chemically creating diamonds on the film, they are much more consistent.

Much of your vintage and modern glass is flame polished...taken up to almost melting point. In some cases being pre-painted with a lower temperature glass glaze.

Some of the crystals are glued in, in which case the standard method is to heat up the case and glass in an oven(some swear by heat gun, I don't*) for maybe 10 minutes and then pushing it out. But on some Seikos (and others)there is a super thin plastic ring that creates the tension on the glass. Those are almost impossible to press out without breaking the glass, as the ring doesn't allow for the same release as the glued in glass. Polishing with the glass in case is almost always a safe bet.

* I look at the "heat the whole thing" method as maximizing the effect of the case expanding faster and farther than the glass. And no, the hole does not expand inward as the case expands outward - basic physics. Heating the glass alone, imo, only softens the glue and allow the glass to expand, while the case remains the same size.

[quietman]

Regarding Cerium slurries I believe that the recommended concentrations are between 1% and 10% by weight which is pretty much what Ed has recommended.

I find from a practical point of view that for me the easiest way to polish is to have a thick paste made up (on my counter-top by the sink) and to apply it to the glass with a wet finger and then to keep wiping the glass with my wet finger. At the 'point of polishing' it needs to be wet but there are many ways of acheiving this. I also find that as the polishing proceeds more water is required simply due to the few degrees temperature rise of the glass drying out the thin layer that has been applied. I also occasionally run my infused cotton wheel under a trickling tap to further moisten things which can't be right

I find that if I apply a correctly diluted slurry to the glass I end up spraying pink spots all over the kitchen wall which eventually results in pain to me

Never been hugely convinced by the added polishing effect produced by the oxidizing power of Cerium on SiO2 glass. I do very much like to reduce my ignorance in these areas though if anyone wants to shine the light.....

[quietman]

As a starter for 10 on mechanical/chemical polishing processes (its not really that interesting....) -

The basic chemical process invovled in Cerium Oxide polishing is an electrokinetic attraction between it and Silicate ions. The generation of the electrokinetic potential requires the presence of water (or some other solvent) and results in a potential inversion of the Cerium Oxide potential as Silicate is adsorbed. So I guess this means that you need enough Cerium Oxide (vs Silicate ions) to prevent over adsorption on each Cerium Oxide particle but enough water to dilute the silicate ion concentration.

I'm not sure how the concentration of the solution affects the 'ionisation' of the Sio2 into aqueous silicate ions in the first place. I would have thought that reduced Cerium solution concentrations would reduce this initiating process?

There was some suggestion that the most efficient silicate adsorption occured in slightly alkaline solutions but that the most efficient measured material removal (actual polishing) occured at neutral or slightly acidic solutions.

I came across some (scientific research papers) references to polishing solutions up to 40% by weight of Cerium Oxide and as low as 0.1% by weight.

Another interesting possibility would be that using smaller Cerium particle sizes would actually increase the glass removal rate due to the increased surface area of an equivalent (by weight) solution concentration. As this doesn't appear to be observed I guess that the dominant polishing effect is the mechanical abrasive one and not the electrokinetic process.

[retroleds]

Regarding Cerium slurries I believe that the recommended concentrations are between 1% and 10% by weight which is pretty much what Ed has recommended.

I find from a practical point of view that for me the easiest way to polish is to have a thick paste made up (on my counter-top by the sink) and to apply it to the glass with a wet finger and then to keep wiping the glass with my wet finger. At the 'point of polishing' it needs to be wet but there are many ways of acheiving this. I also find that as the polishing proceeds more water is required simply due to the few degrees temperature rise of the glass drying out the thin layer that has been applied. I also occasionally run my infused cotton wheel under a trickling tap to further moisten things which can't be right

I find that if I apply a correctly diluted slurry to the glass I end up spraying pink spots all over the kitchen wall which eventually results in pain to me

Pink spots - you can buy white Cerium, slightly more expensive.
Tin Oxide - very white.
Slurry - a crucial stage to not driving yourself crazy is to let the cerium slurry dry onto your felt or leather pad. So it soaks in, rather than just getting pushed or flung off to the side. Then you get the pad lightly wet and start into it. And none of this requires tremendous speed - Dremels are too fast, so are most bench grinders - truly, glass is made up of microscopic high points ^^^^^^^^^^^^^^^^^^^ - high speeds fracture the points. Stones, glass, diamonds - all ground and polished at speeds below 1000 rpm generally.
Considering the amount of work it takes to take out pre-polishing grind marks, I rarely start with anything below 1500 grit on glass. I think there is something to the ionic action of the cerium in right combination of water - they sell it in spray bottles at very low concentrations and you can use it to get off hazing from acid/environment damage. But seriously, Tin oxide works very well, even better on some more minerally, grainy glass. And TO is very cheap.

[quietman]

I have a bit of a 'method' with my not-Dremmel that works well with this.....

I find that Cerium (or presumably TO) polishing works well when some pressure is applied at the point of polishing (at the lower speeds). My little power tool slows down significantly when it is put under torque load by applying pressure to the workpiece. So I usually turn it up almost full speed and then get it running nice and slow by applying it with pressure. Requires some 'feel' to modulate the speed well.

The pressure seems to help but I haven't got any science to back that up......

I didn't want to recommend it but I actually start with 600 grit for really scruffy glass with gouges rather than scratches and it works uniformly and well (I know it kind of shouldn't...)

And there is a huge difference between different 'lots' of carbide paper. I have some that I save for glass because they work smooth and don't let any grit go. And I have some (same store, same price, different back markings and obviously different supplier...) that just drops scratchy grits with no encouragement at all.

I will certainly get some diamond lapping paper when I have a watch worth the expense but alas I think white TO spray up the wall would still result in

[retroleds]

I didn't want to recommend it but I actually start with 600 grit for really scruffy glass with gouges rather than scratches and it works uniformly and well (I know it kind of shouldn't...)

Yeah, 600 makes fast work, but then it takes you a lot more work with the next finer grit. With something like this, at low speed and water, you can take and entire surface down in a few minutes, with nothing as deep as what the 600 would leave.
http://www.ebay.com/itm/NEW-INLAND-FLAT ... 4386cf6f19

THen you switch to this 3000 grit.
http://www.ebay.com/itm/INLAND-SWAPTOP- ... 2418wt_934

And one of the oxides will finish it in a reasonable amount of time: 20-30 minutes. But the two previous steps will have taken less than 10 of actual work time. As a reality check I do all the work with the 2x magnifying visor on, and with bright light available.

Some of this is more m=natural for me...I have done stained glass work as a hobby for years.

[Derek]

quietman - I must admit that I'm struggling with the idea of polishing the glass without removing it first. On my watch, the glass sits proud of the case by maybe 0.5mm. That leaves very little margin for error, before I'm sanding chrome off the case if I happen to tip it by mistake. And then retroleds provides a link to what appears to be a 6 inch sanding disk I'm assuming you won't be attaching that thing to your angle grinder. I must be missing something, because this all seems like very risky stuff indeed.

After 25 years of regular use, my case and buttons are in need of re-chroming. I'm assuming that I'd have to disassemble the case completely, but given retroleds earlier comments about Seikos, it might be a bridge too far. I'd hate to destroy my watch while trying to restore it.

[quietman]

Hi,

I use PVC electrical tape to mask off any adjacent areas when finishing glass thats still in its case (or adjacent areas of steel in different finishes).

If you're not comfortable doing it then perhaps don't.

Rgds,

MP.

[Derek]

Ahh... masking.

Thanks quietman. I knew I had to be missing something obvious.