A question on making ground glass...

[Mark Sawyer]

I've been doing my homework getting ready to make a ground glass or two, and have a question. It's popular for people to use a smaller square of glass to grind the ground glass, using aluminum oxide as the grinding compound. But I was curious... if one used a 5x7 piece of glass to grind another piece of 5x7 glass, would one end up with two serviceable 5x7 ground glasses? Enquiring (and lazy) minds want to know...

[Ari]

I am no expert, but I think you could end up with two 5x7 screens.
All you have to do is maintain perfect, constant and even pressure on the entire surface of both screens...all the time. :)
You will get one good screen and one almost-done screen; you can just go back and grind the missing areas of the second screen, which should take much less time.

[Andrew O'Neill]

Logic says yes.

[Mark Sawyer]

Logic says yes.

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

~ Yogi Berra

[cowanw]

Not so easy to get a good grip and side to side and downward push on a flat piece of glass, without gripping the edges and cutting yourself. A glass puck or in my case a juice glass with a heavy bottom fashionable 29 years ago worked well as a dedicated tool. No matter if the bottom of the glass isn't flat or smooth it soon will be.

[Mark Sawyer]

Good point. I may need to attach a handle with removable silicon or something.

And I expect Ari's right, one screen (or both) may need a little touch-up. Or it may be best using a 4x5 to polish a 5x7 or 8x10. It will be an experimental process...

[Jim C.]

I'd try spray cementing a rubber pad like a mouse pad or yoga mat to a flat board ( melamine coated MDF )
that has a decent handle on it to use on the glass, you'll get a better grip and for pressure, you can place weights
or a sand bag on top.

I had thought of something I came across that I can't remember what it was called, it had a pretty good grippy surface but
wasn't really sticky. I remembered - rubber shelf liner or router pads.
I also thought of suction cups but depending on the thickness you're using it may bow the glass.

[Tin Can]

I have made 5 GG's and taught 2 people do it it. I do not suggest using 2 pieces of identical glass at once. You will find localized unground areas as you check your work in the sink, by completely washing off the grit. Window glass is wavy and needs to be ground flat. Be very careful as you move to small grits to not contaminate with larger grits as you will make scratches.

I use a 3x3" 1/4" piece of glass for the puck, and it gets better with use, and thinner! I use only my fingers to grip the puck. I watch a movie and I'm done.

Crack off the corners first.

I use glass from Home Despot, very cheap and 8X10 and 11X14 is sized perfectly.

I recently bought a 4X5 Satin Snow GG here, just to see how good it was. It is not as good as Steve Hopf's (http://www.hopfglass.com/) and I have bought 3 of them. I hope to achieve his results one day...

I compare GG's first by looking at a bright light with them held in my hand, then mounted in the camera.

[Jody_S]

I think you will find it impracticable unless you use a large quantity of very liquid AlO slurry. With smaller, denser pastes, the two glass surfaces stick together, and 2 5x7 glasses will possibly break from the suction at some point in your grinding.

[Tin Can]

I think you will find it impracticable unless you use a large quantity of very liquid AlO slurry. With smaller, denser pastes, the two glass surfaces stick together, and 2 5x7 glasses will possibly break from the suction at some point in your grinding.

+1.

[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.

[Ari]

Slight left turn.
A question for the "survivalists":
Suppose you were out of town/out of country and broke your GG; you were able to find a piece of glass that fit your camera (picture frame or something), but didn't have the required grit compound with you.
What everyday item could you use in a pinch to grind the glass in order to make it usable enough? Toothpaste? Talcum powder? Fine sand?

[Mark Sawyer]

Slight left turn.
A question for the "survivalists":
Suppose you were out of town/out of country and broke your GG...

This happened to me many years ago, when I was doing field photography at a dig for the National Park Service. Someone knocked my camera over and broke the GG. I bought a piece of glass and a can of glass frosting at the closest hardware store. It worked fairly well, disaster averted. I later bought a replacement "real" GG, and a fine-sanded polycarbonate acrylic emergency GG for my field kit.

[Peter De Smidt]

Satin tape.

[Ari]

Satin tape.

Is that like Scotch tape?

[Peter De Smidt]

Yes.

[Jim Jones]

Valve grinding compound? Maybe still available in auto parts shops.

[cowanw]

Satin urethane spray paint, fish tank frosting,600 grit sandpaper, and if in South Africa, diamond dust.

[Mark Sawyer]

From what I've read, valve grinding compound is too course and leaves lots of little chips in the glass. Also from what I've read, many people use it anyways...

[Peter De Smidt]

Valve grinding compound is better than nothing...but tape is better, and much easier, in a emergency.

[HMG]

http://www.apug.org/forums/forum216/78392-making-ground-glass-focus-screen.html

I've made a ground glass with rock polishing grit (since I had some around). Seems OK.

[Eric Biggerstaff]

I make my own and the key is getting even pressure on the grinding glass, the smaller piece. The larger piece of glass you use to grind with, the less even the pressure becomes. A smaller piece allows you to apply more even and consistent pressure while you grind, at least that is my experience. Also, as noted, while you grind the slurry begins to dry and the glass will begin to stick so you want to be able to remove it easily. All in all, it is not a difficult thing to make.

Also, I keep frosted Scotch tape in my repair box in case I crack a ground glass, it works well in a pinch. I was out yesterday with a friend and his 8X10 blew over and his glass shattered, not much we could do with that except head home.

[IanG]

http://www.apug.org/forums/forum216/78392-making-ground-glass-focus-screen.html

I've made a ground glass with rock polishing grit (since I had some around). Seems OK.

I make around 100+ screens a year using the method you've linked to. I started because I realised I needed around 10 screens and that was going to be expensive buying from the US. These days I either make new screens or regrind the old ones for all my restorations.

Back around 2008 I posted a thread on APUG comparing various screen brightnesses, basically I found a huge difference between screen. I put my Crown Graphic alongside my Wista with it's original composite fresnel screen both with 150mm lenses and there was around 4 stops difference. This was making the Crown Graphic hard to focus particularly as I usually had to use it hand held it already had a replacement screen from a leading US supplier (not Satin Snow) and I re-ground it and it was significantly brighter, I also added a fresnel, now it's only about 2/3rds of a stop less bright compared to the Wista.

Ian

[Tin Can]

I make around 100+ screens a year using the method you've linked to. I started because I realised I needed around 10 screens and that was going to be expensive buying from the US. These days I either make new screens or regrind the old ones for all my restorations.

Back around 2008 I posted a thread on APUG comparing various screen brightnesses, basically I found a huge difference between screen. I put my Crown Graphic alongside my Wista with it's original composite fresnel screen both with 150mm lenses and there was around 4 stops difference. This was making the Crown Graphic hard to focus particularly as I usually had to use it hand held it already had a replacement screen from a leading US supplier (not Satin Snow) and I re-ground it and it was significantly brighter, I also added a fresnel, now it's only about 2/3rds of a stop less bright compared to the Wista.

Ian

Ian's APUG tutorial is the post that got me making GG. I love making them and have been considering regrinding a few of my factory GG.

I recenty bought finer grit. Maybe tonight!

Thanks Ian.

[cowanw]

Ian's tutorial got me started too.
Finer grit is a trade off of a more evenly spread visualization versus a decrease in brightness. Coarser grits can be very bright. Fresnels are a whole other issue. but I think everybody has a way of seeing that is unique. some don't mind a hot spot with a bright screen and vice versa.
Be interested to hear if you do some finer grits.
For more bucks though the fine plastic Fresnel/GG's, are nice.

[Tin Can]

Ian's tutorial got me started too.
Finer grit is a trade off of a more evenly spread visualization versus a decrease in brightness. Coarser grits can be very bright. Fresnels are a whole other issue. but I think everybody has a way of seeing that is unique. some don't mind a hot spot with a bright screen and vice versa.
Be interested to hear if you do some finer grits.
For more bucks though the fine plastic Fresnel/GG's, are nice.

I am gentle with all equipment and don't backpack. I think mountain climbers absolutely need plastic and fresnel GG. I haven't YET broken a GG. Knock on wooden head.

[cowanw]

I wasn't thinking of breaking, but of the combination of brightness, and lack of a hot spot without troublesome Fresnel lines as with my other cheapo Fresnel's.

[WayneStevenson]

To answer your thought experiment? Hobby stores carry acid etching for glass. Works great. Even Walmart carries Testor's Dullcote. It's a clear matte spray found with the model kits. Hairspray would likely work just as easy.

If you like going to go the easy route for a great finish, sandblast your glass. Go through a hopper of rough, and a hopper of fine and you're good to go.

[Peter De Smidt]

Wayne, you've had good luck with the acid? I tried it a bunch of ways some years ago, and I couldn't get even results.

[WayneStevenson]

You know it has been almost ten years probably since I used the acid. And it was a challenge to get great results as it did require practice. Though usable results are instantaneous to get you through.

The etching bath I found worked better than the cream, unless the cream was diluted with water. Though the cream sometimes had chunks in it so you had to be creative in ways to get them worked out. And you had to do a few coats.

[JoeV]

I made a crude "ground plastic" from an 8.5"x11" plastic fresnel magnifier, purchased at Staples office supply store, for a homemade 8x10 box camera. The fresnel's reverse side is smooth, so I ground it using a random orbital sander and 600 grit emory. The result is a one-piece GG+fresnel that's still serviceable today. Sure, it's not as flat as a true glass GG, but flat enough, and lots cheaper. And I'm shooting paper negatives, so it's not like I'm wasting $8+ sheets of film with each shot (but that's a subject for another thread...).

~Joe

[bvaughn4]

Just to add something that made my experience much easier when I made a couple of 8x10 screens - I used one of these suction cup handles on a 3"x3" piece of 1/4" plate glass. Much easier to grip and apply pressure at same time. Hope it hasn't already been referenced called myself looking at each comment.

http://t.harborfreight.com/suction-cup-with-quick-release-46900.html

[Ari]

Hairspray, Dullcote, Staples magnifier: great ideas, thanks!
I'm keeping Scotch tape in my bag from now on.

[Robert A. Zeichner]

I have used an old 2"x2" Tiffen filter (flat and thick enough) with a golf ball cemented to it with JB Weld. The golf ball makes for a very comfortable handle. With this combination, I have gotten great results making both 4x5 and 5x7 ground glass. As a work surface, I use a slab of 3/4" plywood covered with a few layers of newspaper. When the paper gets wet from the grinding slurry, everything stays in place while I grind away.

[Nodda Duma]

I've been doing my homework getting ready to make a ground glass or two, and have a question. It's popular for people to use a smaller square of glass to grind the ground glass, using aluminum oxide as the grinding compound. But I was curious... if one used a 5x7 piece of glass to grind another piece of 5x7 glass, would one end up with two serviceable 5x7 ground glasses? Enquiring (and lazy) minds want to know...


Yes. Use normal center-over-center polishing strokes for maybe 10 minutes, then flip them over so that the glass on bottom is now on top (grinding surfaces still sandwiched in the middle), and repeat. The flipping over is important to maintain flatness. Otherwise you start grinding out a spherical surface. Continue these steps until the surfaces are satisfactorily ground.

Random link showing the grinding strokes: http://www.fvas.net/victor/mirror.htm

[Jim Jones]

Using two blanks the same size in hopes of getting two good ground glasses demands two very flat blanks. It may be faster to grind just one GG at a time. A smaller tool can conform to the deviations in flatness that are too slight to affect GG performance.

[Nodda Duma]

Using two blanks the same size in hopes of getting two good ground glasses demands two very flat blanks. It may be faster to grind just one GG at a time. A smaller tool can conform to the deviations in flatness that are too slight to affect GG performance.

Actually, when talking about grinding/polishing optical flats, using blank and tool (or two glass plates in this case) of the same size is what leads to perfectly flat surfaces. Undersized grinding / polishing tools just aren't used in an optical shop at the sizes we're talking. An optician can't afford to monkey around like that if he can just use the same size tool. Not to say the OP needs that precision of flatness but why make it harder? As soon as the whole surface frosts over he's done. That's not a function of how flat the plates start out.

The key in hand grinding (or polishing) a flat surface is to use the appropriate grinding stroke and a rigid base to set the glass on. That stuff can be looked up on the web. I've found that periodically reversing which glass piece is on top (maybe once every 10-20 strokes) makes it easier to grind flat as well.