Buy grit for grinding ground glass in EU?

reddesert

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I looked at the dokasphotos article. While I understand his argument for using aluminum oxide, I also think he started with too coarse a grit of silicon carbide. I made a ground glass using 600 grit silicon carbide (which is about the same size as the 5 micron aluminum oxide) and it's very nice. It also doesn't take forever.

I am in the US and I bought about 1 lb (~ half kilo) of silicon carbide locally from a tool store that has supplies for jewelry makers and rock-polishing/geology enthusiasts. 500g of SiC cost about US$8 and would be enough to grind hundreds of ground glasses. It is not difficult, just takes a little patience.
 

awty

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I just use the stuff from rock polishers, easy to get hold of. Think I have 300 grit, but would have to check. It's easy peasey to make your own ground glass, the hardest part is cutting the corners. Use a quality glass cutter and a glass file.
 

Christopher Walrath

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I have, in the ancient past, used valve lapping compound that you can get in most non-bigbox auto parts stores.
 

mshchem

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Yep, go to a lapidary hobby shop. I've used carbide, works really fast. Finer is slow and makes pretty gg.
 

DREW WILEY

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Look up Lapidary suppliers - rock polishing. Or even granite countertop fabrication suppliers. Oh --- others beat me to it.
 

mshchem

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DREW WILEY said:
Look up Lapidary suppliers - rock polishing. Or even granite countertop fabrication suppliers. Oh --- others beat me to it.
Click to expand...

Great minds think alike! I do remember looking at a 1940's photo magazine on making ground glass by combining Mallinkrodt roach powder (sodium fluoride) with glacial acetic acid to make home brew hydrofluoric acid. What could go wrong
 

DREW WILEY

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My father and grandfather were rock hounds with polishers. Lots of agates, sagenite, etc. Then in college geology classes the rock sections were cut so thin that, after polishing they were translucent, allowing examination for micro-fossils or mineral polarization etc.
 

TheYoungPretender

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You could try ventilslippasta (valve grinding compound?). The one sold at Biltema works fine but I imagine you would be able to find it at other places as well.
 

koraks

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At some point, I decided to do a head gasket replacement on a car I owned, and in the process, I also ground the valves for perfect seating in the head. For this purpose, I bought some grounding compound, which I kept around ever since. The valve grinding thing was a one-time project. But since, I've used the same stuff to grind some glass multiple times. Mind you, I needed the glass as a diffusor, not as a camera ground glass. I'm sure it would work in the latter capacity as well, but haven't specifically tried it.

The morale of the story is - don't get too hung up on application-specific materials. More often than not, you pay for someone grabbing a generic material off the shelf and sticking a label onto it that says "Specifically for grinding view camera glass".
 

Jonathan-sv

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TheYoungPretender said:
You could try ventilslippasta (valve grinding compound?). The one sold at Biltema works fine but I imagine you would be able to find it at other places as well.
Click to expand...

I did some with Biltema's valve grinding compound and it was a bit coarse, but the ground glass did work. I think I read somewhere it is around 320, which is a bit on the coarse side. I just ordered some 600 and 800 but it is 500 g each which will last basically forever.....
 

eli griggs

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Contact an astronomy club or two, as these guys and gals are making their own telescoped and grinding their own lenses and perhaps mirrors.

They'll be a big help.

Or buy some high quality sand paper.
 
OP
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-chrille-

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bernard_L said:
Eleven days gone by.
Looks like the OP has left the room.
Photrio answering service. How can we help you?
Click to expand...

Time just flies by but I also have a life outside the Photrio universe Sooner or later I always come back and tell you how it went or just say thanks to everyone who was helpful and replied to my questions.

In this case I went for the aluminium oxide route. I got an offer from Stathis Firstlight yesterday
 

koraks

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Oh yeah, cool! Good luck. I always find that getting started is the challenging bit. Once you break the shiny surface, it gets easier.
 

Kino

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A cheap suction cup helps in moving the glass around...
 
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-chrille-

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Finished ground glass
 

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koraks

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That looks really good! How did you manage to use that Logan matte cutter for this purpose? I've got the same (or very similar) one; it's not a suction cup; did you just 'stick' it onto the glass with moisture? Or double-sided tape? It does make a great handle!
 

eli griggs

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I think either thin Scotch type double stick or thin adhesive glue would be perfect.

Those Logan matt cutters are very smooth and polished bottom surfaces and slide on matt papers, etc easily.
 
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-chrille-

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Yes, double sided Scotch tape. Easy to remove from the anodized aluminum matte cutter but strong enough to hold the grip on to the glass plate.

The surface of ground glass is really smooth. I think Dokas article is correct stating you get a very smooth and super bright ground glass with aluminium oxide.

I highly recommend using aluminium oxide even if it took me almost 2 hours of grinding. Actually it was pretty fun seeing the surface slowly appear while listening to Quinn Jacobsons wet plate discussions on youtube.
 
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-chrille-

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I replaced the original ground glass on my Intrepid 5x7 with a DIY ground glass grinded with 5 and 3um aluminium oxide and here is a comparison. I also did some measurement with my Sekonic L-308X of brightness between these two with artificial lighting condition but could not measure any difference.

The DIY ground glass makes it easier to focus on fine details, very useful when I do portraits with short DOF.

(Iphone SE with Pentax 4x loupe. Intrepid ground glass with grid screen)

 
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-chrille-

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… and no more grinding by hand Safety first if you do something like that thought!
 

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