Making ground glass?
Clyde Soles
your own groundglass. My dad has a sandblasting rig and has done a lot of etched
glass art projects. I was thinking of having him make me a few different samples
for my 7x17 to see if I could improve brightness. Does anyone have any
experience with this? Is the Beattie screen a special material?
Larry Whatley
: All this talk about 4x5 unsharpness has made me wonder how hard it is to make
: your own groundglass.
I have used sand-blasted glass for an enlarger diffuser--it's very
economical-- but normally it's much too coarse to use for focusing.
I don't know just how fine sandblasting can be done, though.
- Larry Whatley
Irv M
>All this talk about 4x5 unsharpness has made me wonder how hard it is to make
>your own groundglass. My dad has a sandblasting rig and has done a lot of etched
>glass art projects. I was thinking of having him make me a few different samples
>for my 7x17 to see if I could improve brightness. Does anyone have any
>experience with this? Is the Beattie screen a special material?
If I remember correctly, camera ground glass is flouride etched (I may
be wrong here,)
Mike Paton
: Clyde Soles (Clyde...@nile.com) wrote:
: : All this talk about 4x5 unsharpness has made me wonder how hard it is to make
: : your own groundglass.
: I have used sand-blasted glass for an enlarger diffuser--it's very
coo...@peg.apc.org
following method. The basic principle is to grind to pieces of suitable
glass (window or picture depending on your preference for thickness, 4x5
3 pieces cost me $2 recently) against each other using a
grinding/abrasive paste/powder and suitable lubricant (obviously one
face on each piece of glass only).
[SOME BACKGROUND: Because of my work (pathology lab) I used an abrasive
powder that is used on large glass plates on which steel microtome knife
blades are sharpened. The lubricant is water in this case. The idea came
to me one day when looking at the finely ground surface of these large
glass plates.]
The technique is to lay one sheet of your glass on a firm flat
(waterproof) surface, sprinkle on some abrasive over the whole surface,
add water, lay the other sheet on and rub the top sheet against the
bottom in a random-"circular" motion ( not a whole lot of precision
required here!). Repeat the above steps, stopping from time to time to
rinse off and check the evenness (corners are a little slower to come up)
and the "depth" of the grind. Takes 15-20 minutes.
I am happy with the coarseness-fineness of the results but I guess a
finer powder would give a finer grind and (?)better resolution. I feel
sure there are other industries that would use suitable abrasive
compounds, perhaps even a common abrasive cleaner could be an option (
One that DOES scratch bench-tops!) I understand there is/was a product
called "jeweller's rouge" that is an extemely finely-divided abrasive
(?too fine) used by manufacturing jewellers.
Markings for Polaroid or rollfilm backs can be made on the ground side
with a fine lead/graphite pencil or a "Sharpie". A coating of linseed oil
allowed to dry (days to weeks) gives a slightly more brilliant image and
a little protection to the grind.
Final tip: For a transient bright image (close to aerial image
brightness) WET a spot on a plain (non-oiled) GG with water (or at a
pinch: saliva) Is the drool obvious, miss?
Now back in our time machines and return to Beattie, Sinar, and care with
bodily fluids!
PTC
mike...@austin.ibm.com
In article <31c7cc$113b...@royal.lanyap.com>, i...@ellijay.com (Irv M) writes:
> Clyde...@nile.com (Clyde Soles) wrote:
>
> >All this talk about 4x5 unsharpness has made me wonder how hard it is to make
> >glass art projects. I was thinking of having him make me a few different samples
> >for my 7x17 to see if I could improve brightness. Does anyone have any
> >experience with this? Is the Beattie screen a special material?
>
> If I remember correctly, camera ground glass is flouride etched (I may
> be wrong here,)
>
>
Probably hydroflouric acid. Use to etch silicon dioxide for semi-conductor
manufacture. I have heard that you can make a decent ground glass by
grinding the glass with the finer telescope grinding componds as well as
valve-grinding compound. Don't use the acid. VERY NASTY.
--
Michael (Mike) C. Dean
IBM - RISC/6000 Division
Austin, Texas.
Disclaimer - The opinions expressed in this append are mine alone.
peters
>Clyde Soles (Clyde...@nile.com) wrote:
>: All this talk about 4x5 unsharpness has made me wonder how hard it is to make
>: your own groundglass.
>I have used sand-blasted glass for an enlarger diffuser--it's very
>economical-- but normally it's much too coarse to use for focusing.
>I don't know just how fine sandblasting can be done, though.
>- Larry Whatley
You can make your own groundglass by taking two thin pieces of glass,
spreading valve grinding compound between the two and rubbing them in
a circular pattern. "Standard" valve grinding compound gives glass
that is usable, but too coarse for easy focusing. I have seen a
"fine" grade of valve grinding compound sold, but haven't tried it.
Will next time. Robert Peters
COUGER GORDON
peters <to...@oz.net> wrote:
>lar...@lsid.hp.com (Larry Whatley) wrote:
>
>>Clyde Soles (Clyde...@nile.com) wrote:
>>: All this talk about 4x5 unsharpness has made me wonder how hard it is to make
>>: your own groundglass.
>
drops of 20 weight motor oil on the glass a dab of fine valve grinding
compound. Move you finger so you don't rotate the glass too long in one place.
Wash off the compound and oil in kerosene when it looses it cutting action,
you can feel it. Continue until you have the degree of grind that suits you.
If you are particular about flatness use three pieces of glass. Grind a on b
b on c, c on a and so on.
Good luck
Gordon.
PS if you start with a courser grit and go to a finer grit be very careful
in cleaning up all the old larger grit.
Gordon Couger
Biosystems & Agricultural Engineering. 114 AG Hall Stillwater, OK 74075
gco...@master.ceat.okstate.edu 405 744 8392 day 625-2855 evenings
san...@suzy.torolab.ibm.com
: All this talk about 4x5 unsharpness has made me wonder how hard it is to make
: your own groundglass.
Check out any good book on telescope making (grinding the mirror section)
it should cover all of the stuff needed (grades of grit, proper motion of
the two sheets of glass for maintaining a perfect plane (as opposed to the
spherical and then parabolic sections you'd want for a mirror),
The only reference I could find handy (and not the one I have at home):
"How and Why to Make a
User-Friendly Sidewalk Telescope" by John Dobson with Norm Sperling.
Sandor
Dion Johnson
about abrasives:
Jeweler's rouge is too fine.
You can get carborundum powder at rock polishing hobbyist supply
stores. About #400 is pretty good. #600 is almost too fine.
Diamond dust works faster, but is rather expensive. Also it has
a funny coarseness grading system and I didnt have time to
figure out which was the right one. If anyone has used it
successfully, it would be interesting to know which grade to
use.
The acid etched glasses, if you look at them closely, are wavy,
not really all that rough at the surface. If you want a nice
bright image, the grinding method works very well; creates a lot
of reflective irregularities at the surface.
-Dion