Glass Restore - Cerium Oxide

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ablumny
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Post by ablumny » Sat. Oct. 25, 2014 6:47 pm

Heading into our 7th season with our DVC500. Tried many times over the years to keep the glass clear but always gave up. Stumbled across a YouTube video where a fella was restoring is wood stove glass. Starts with a bath of Muriatic Acid, neutralized with baking soda, cleaned with water. Then with a paste of Cerium Oxide powder, polish polish and polish. My glass is pretty far gone but its way better then when I started. I think if I gave it a couple of hours I may have seen more improvement.

The acid is available at Home Depot or Lowes. Gloves and a mask !
I had to order the Cerium Oxide on line (eBay) and it came with the 4" felt wheel.

Thought it may help someone...
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Before

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Cerium Oxide Paste

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After 20 mins of polishing

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mozz
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Post by mozz » Sat. Oct. 25, 2014 8:22 pm

It looks like some polishing compound I have for the car. Correct that, rubbing compound, I think. Maybe annual maintenance would make it easier on the glass?

 
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ablumny
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Post by ablumny » Sun. Oct. 26, 2014 8:30 am

Ha looks like rubbing compound when you mix it up. Apparently it's commonly used in auto glass restoration. Anyway, yep I was staying on top of it for the first couple of years but let it go when it starting getting worse.
Ab

 
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lsayre
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Post by lsayre » Sun. Oct. 26, 2014 9:10 am

ablumny wrote:Ha looks like rubbing compound when you mix it up. Apparently it's commonly used in auto glass restoration. Anyway, yep I was staying on top of it for the first couple of years but let it go when it starting getting worse.
Ab
It's what most of us parabolic mirror makers use to polish out telescope mirrors. The tool for this is made of dental grade plaster coated with roughly 1/4" of pine tar pitch. The cerium oxide is wetted and placed onto the mirror, and the pine tar pitch tool is worked over the surface, whereby it slowly takes on the shape of the surface and then the Cerium Oxide does its thing and polishes the mirror smooth.

For those of you who are wondering, there is no means by which you can straight up grind a see-through clear finish into glass. Even the finest grits available will leave you with a completely frost covered piece of glass.


 
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ablumny
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Post by ablumny » Sun. Oct. 26, 2014 12:05 pm

I didn't think so either and if your in the mirror making biz you're certainly more expert them I am but this guy In the YouTube video puts up a compelling story..... And I have to say the areas of my glass that weren't so far gone on the bottom came out perfectly clear. Small investment to get any improvement I suppose IF it evens matters (which it did to my wife! :D

https://m.youtube.com/watch?v=fob94kf7eSs

 
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Post by lsayre » Sun. Oct. 26, 2014 12:35 pm

The soft sanding disk accomplishes much the same effect as would pine tar pitch. Since you are not "figuring" the glass, but rather merely polishing it, this method is fine. But if you were shooting for a surface "figure" that has all of its peaks and valleys no taller than 1/10 of one wavelength of green light (500 nanometer light frequency) you would fail miserably via the video method. Telescope mirrors are figured across their entire surface to a level of perfection that is roughly +/- 2 millionths of an inch. No mechanical method of measuring (that I'm aware of at least) can measure down to that level of perfection.

 
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Post by tsb » Sun. Oct. 26, 2014 12:54 pm

A long time ago in another life, I went to the star party at Stellafane in Vermont.
I watched a guy make a very respectable mirror out of a pyrex pie plate in about
3 hrs. He used it that day to observe sun spots and put the aluminum on the next
morning.

 
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Post by lsayre » Sun. Oct. 26, 2014 12:59 pm

It can be done. If it was small enough and its focal length was also long enough, he could achieve 1/10 wavelength of green light precision with it being merely spherical. (spheroidal). A purely spherical 6" F/10 mirror (60" focal length) just about meets the necessary criteria, but does fall short, and will exhibit noticable spherical aberration. A 6" F/12 (72" focal length) will just barely meet the required optical criteria if left spherical. Otherwise he had to use a Foucault Tester to figure (push) it into a paraboloid.


 
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Post by tsb » Sun. Oct. 26, 2014 1:28 pm

It was a 9" pie plate. I think he was shooting for f12.

 
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Post by ablumny » Sun. Oct. 26, 2014 8:44 pm

lsayre wrote:The soft sanding disk accomplishes much the same effect as would pine tar pitch. Since you are not "figuring" the glass, but rather merely polishing it, this method is fine. But if you were shooting for a surface "figure" that has all of its peaks and valleys no taller than 1/10 of one wavelength of green light (500 nanometer light frequency) you would fail miserably via the video method. Telescope mirrors are figured across their entire surface to a level of perfection that is roughly +/- 2 millionths of an inch. No mechanical method of measuring (that I'm aware of at least) can measure down to that level of perfection.
I was shooting for a good enough result that made my wife happy and didn't cost me $100 for new glass ! Cool info though ... :D

 
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Post by Rick 386 » Sun. Oct. 26, 2014 10:04 pm

ablumny wrote:Ha looks like rubbing compound when you mix it up. Apparently it's commonly used in auto glass restoration. ......
Don't know f this is the same stuff they used to use or not on auto glass, but some caution may be necessary to not ingest any dust from the compounding process. And it may be wise to wear some gloves as well.

Some of those products were not too good for your health.

Rick

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