Originally Posted by
Christopher D. Keth
This is the way I do it. I'm sure there are many ways and probably better ways but this works for me. The thing to keep in mind all the while you read this is to take your time. This process is meant to create uniform little conchoidal chips in the glass. If it's done right, they will essentially act like little surfaces for the image but also pass a maximum of light. If you get in a rush or try to apply too much pressure, you will end up with an uneven glass or a ground glass with bigger or uneven little chips. It will work but won't be as bright as one done with care.
First, I cut the glass to size and clip the corners. I've been told you can cut the glass after grinding but I ruined 2 glasses that way and never tried a third time. I believe the people who say it can be done, but I can't figure it out. The cut keeps wandering. Cut 2 pieces of equal size. One will be the one you concentrate on grinding. The other will be the tool you grind with. In practice, you should end up with both of them ground to satisfaction so you can have a spare. If you do this, make sure to clip the corners on both pieces and test fit them into your camera before expending the effort.
Second, you will want to get your work area prepared. Lay a couple of sheets of newspaper out on the table. They will keep everything clean and help the glass to not slide around. You will want a bowl of water handy, with a spoon in it to dispense the water, as well as the grits you will use. I like aluminum oxide in 5 micron and 3 micron sizes. I got a pound of each at a lapidary shop and barely used any to grind a half-dozen glasses for myself and a couple of other people.
With your spoon, put a few drops of water on the newspaper and set one piece of glass down. The water just sticks it down to the paper. Put a couple pinches of 5 micron alox on the glass and then pour a spoonful of water over it and stir it a bit with the spoon. It should make a thin slurry with enough grit to more than cover the glass. You'll get the feel of how thick or thin it needs to be pretty quick. Lay the other piece of glass on top and with what I can only describe as "a medium finger pressure" start grinding it in a circle. When the glass doesn't want to move against the other piece anymore, the slurry is drying up and you need to add more water. If the slurry is looking too thin, add a pinch of grit. It's kind of a go by eye thing.
Grind grind grind...Check the pieces from time to time. They will start by grinding unevenly in patches. That is the stage where you are flattening the waves out of the glass. At some point, you will check the pieces of glass and they will be evenly frosted from edge to edge. At that point, take both pieces of glass to the kitchen sink and rinse all the grit off. Rinse some more. You want to get ALL of it off or it will just put scratches in the 3 micron grind. After rinsing wash them with dish detergent and set them aside to dry.
Now go clean up the work area. Replace the newspaper and the bowl of water. Wash the bowl and spoon, too. Everything should be new to make sure you have no 5 micron grit hanging around.
For the second stage, do everything as you did before but with the 3 micron grit. Apply less pressure, only enough to be able to move the top glass in relation to the bottom. More will create scratches or tiny chips that will degrade the quality of the glass. As you go with this second stage, you will be able to see the finer grind of the 3 micron in contrast to the grind of the 5 micron. It is subtle but able to be seen. Once both pieces of glass show this fine grind evenly, you are done.
I line my glasses with a .5mm mechanical pencil. It is easy to see while also being unobtrusive to viewing the image as a whole. If you want a bolder grid, .3mm drafting pens work well. Draw the line quickly or the ink can bleed and make an uneven line.
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