U of S | Mailing List Archive | alt-photo-process-l | Re: printing gum on glass

Re: printing gum on glass

When leafing glass, the usual cleaning regimen is to scrub with bon ami cleaner, it won't scratch the glass and it gets everything and anything off.


Robert wrote:
I clean glass by washing in warm warder with Oxiclean. This works well.

Best regards,

-----Original Message-----
From: Katharine Thayer [mailto:kthayer@pacifier.com] Sent: Thursday, July 19, 2007 1:37 PM
To: alt-photo-process-l@usask.ca
Subject: Re: printing gum on glass

To address Judy's suggestion earlier about Christopher James' first editiion: no, there's not a chapter on printing gum on glass per se in the first edition. There's a section on printing gum on "alternative surfaces, such as metal plates, stone, chalkboard slate, glass, mica, vinyl or plastic" which addresses different ways to introduce tooth to hard surfaces, including abrading the surface or (more relevant to glass) subbing the surface with material that will help the gum adhere. He doesn't (by my reading) repeat or deny any myth about midtones and gum on glass, which by the way is a myth I've never encountered. There is also a separate section about printing on glass, not geared to gum especially, which gives Galina's method of subbing the glass with gelatin.

It's no particular myth that gum doesn't adhere well to glass because of the slick surface of the glass which offers no tooth for the gum to hang onto, and as James indicates, the glass usually needs to be treated in some way to increase the adhesion of the gum to the glass. Some people use silane very effectively for a sub on glass for gum printing. I have used a light dusting of fine pumice in acrylic medium, for a sub to provide tooth for printing on glass.

The glass must be scrupulously clean; I find a final swash of 200- proof alcohol works very well to remove every trace of whatever cleaning material may be clinging to the surface after complete rinsing; when it sheets cleanly off the glass without beading or catching anywhere, you know the glass is clean. Then a sub, of whatever works for you, and then expose the heck out of it (someone told me this once a long long time ago and I didn't believe him, but indeed, an extra-long exposure does increase the likelihood of retaining the hardened gum on the glass) and then develop very very gently, face up, with fingers crossed.

Or, as Marek suggests, expose from the back.