AFAIK, the last commercially made glass plates were Kodak, 4x5 inch,
T-Max 100, sold mainly for astronomy.  They were discontinued in 1999 or
2000; even astronomers are using sheet film (when they use film at all)
these days.

You'll want ordinary float glass, 2 mm thick.  Which is a problem,
because the thinnest size you can get from glass shops these days is 2.5
mm.  You might check with companies that sell (or preferably
manufacture) microscope slides; those are 1 mm glass, and a source for
that thickness might well have it in 2 mm as well.

You can carefully clean the plates, including a final rinse with sodium
hypochlorite solution (aka chlorine bleach), sub with photographic
gelatin, and then coat with Liquid Light or other liquid printing
emulsion.  You'll get a more or less orthochromatic (red-blind) coating
with ISO speed between 1 and about 6, depending on the brand and age of
the emulsion you use.  You'll still have trouble with the emulsion
lifting, most likely.  You'll find the usual problems encounterd in
printing color negatives to B&W paper -- muddiness and poor scale
rendition, because the liquid emulsion is polycontrast, and colors in
the scene will cause local contrast changes just as filters would in
printing.

Alternately, you can learn wet-plate processing, though if your camera
isn't designed for wet plates it'll be difficult to coat, sensitize,
load, expose, and develop before the plate dries (after which it's
impossible to develop because the water solution won't penetrate the
collodion surface after it's dried).  Or you can try to research the
collodion dry-plate processes -- but you'll still wind up with an ortho
or even purely blue-sensitive coating; I don't know of any panchromatic
coating being produced before gelatin dry plates were introduced around
1880, and ortho (both plate and film) was still common even after the
First World War.

You could even learn Daguerreotypy, though I wouldn't recommend it --
chlorine and bromine aren't all that hard to deal with, but mercury
vapor is very, very nasty, and cumulative.

What most people do is to source film sheaths and use modern sheet film.
 A film sheath mounts in the holder like a glass plate, but carries a
sheet of film; it's effectively an adapter to allow an old style holder
to be used with modern materials; this will (depending on format and
your budget) allow you to use up to ISO 400 materials in B&W, color
negative, and color positive transparency (aka reversal).

bk a écrit :

Hi !
Slightly OT but....
I use mounting board of the correct thickness put at the bottom of the
films holders (painted flat black with a marker) above which I put
regular sheet film...
Hope this helps ;-)
Oh BTW, Slavish (Russia) manufacture glass plates (look at
retrophotograpic in Great Brittain)