A question on making ground glass...

[Jim Jones]

I've used picture frame glass for focusing screens. It's thinner than hardware store glass. Although the glass looks even, using two equal size sheets in hopes of saving labor in making two screens quickly reveals waviness. However, if the puck is cut to a common small format size, it may be useful at some later date. The sharp edges of glass should first be slightly dulled with something like an old whetstone. I do this for the glass in picture frames, too.

[aclark]

Artists who make their own oil paint use a glass muller to grind the colour pigment on a glass slab. The muller looks a bit like an inverted mushroom, the "stalk" acting s a comfortable handle. I imagine it would work very well for making ground glass. Mullers come in different sizes and are available from art suppliers.
I've only made one ground glass - a 10"x8". I used 2mm picture glass and ground it with a 900 grit Japanese water stone - a whetstone used for sharpening woodwork plane irons and chisels. It came out fine. I simply placed the glass on a flt surface and kept rubbing it all over with the waterstone until I'd got an even ground surface. Waterstones are kept saturated wet. Mine lives in a plastic box topped up with water. In use the particles break free so you get a good slurry build- up.
A Japanese waterstone costs about the same as a glass muller, and is just as easy to hold. However, if you go down the muller route, then you have to buy the grit as well. But you could then experiment with different grades.

Alan

[Michael Rosenberg]

Check out the article by Dick Dokas. : http://www.dokasphotos.com/techniques/ground_glass/

Mike

[Old-N-Feeble]

When I was a little tyke my father taught me how to evenly hand-polish the cut side of a geode with the least effort. He used a piece of flat steel significantly larger than the face to be polished and let the weight of the stone do the hard work.

I would probably use hot wax to attach the glass to one piece of perfectly flat steal and turn that sandwich glass side down onto another piece of perfectly flat steel with the grinding compound in between. Let the weight of the glass and steel do the hard work... not TOO much weight though. This method should eliminate uneven pressures. If it were me I think I'd look for a vibrator of some sort to place the entire stack on. Then I'd turn on the switch and walk away for awhile. Then again... I'm lazy.

[ndrs]

Check out the article by Dick Dokas. : http://www.dokasphotos.com/techniques/ground_glass/

Mike

I do it exactly like this. Glass is placed on wet newspaper to keep it in place.
Get good quality glass. Cheap one, like from inexpensive picture frames, is often wavy and you'll need much more elbow grease to get an even suface.

[Andrew O'Neill]

"In theory, practice and theory are the same thing. In practice, they aren't."

~ Yogi Berra

"It's because I'm smarter than the average bear."

~ Yogi Bear

[Mark Sawyer]

Thanks to all for the input! Very goods points that will be taken into consideration! I'll probably go with a 4x5 puck to grind a larger piece.

[goamules]

I've made a few using the .0002 Alum Oxide grit as Dokas describes. I think the larger the square inches of the grinding jig glass, the harder you will have to push. It will be diminishing returns. I use a 3 or 4 inch piece. I don't start with rough grit either. I only use the .0002 stuff, and in 1 hour have a good 5x7 done.

[cowanw]

The coarser the grind the brighter the image but the more a center spot dominates.
I have wondered if a 2 grit surface might be an idea worth pursuing; that is, a fine ground centre circle area and a courser ground peripheral area, but have not done it yet.

[William Whitaker]

Pitch is used in lensmaking to attach glass to glass or most anything (such as a handle) to glass. Pitch melts easily and can be broken free when chilled (time in the freezer). But attaching to a thin piece of window glass might invite the glass to give way first. Mark, you live in the center of the universe for optical work. Wander over to the optics lab on campus and ask someone there. (I miss Tucson!!)

FWIW, I've used #500 carborundum for making ground glass and found it worked very well.