Contact printing glass plates...?

[Randy]

With modern films it's pretty easy to maintain flatness / contact between the film and paper by using a heavy sheet of glass or a contact printing frame. How would one maintain uniform contact with a thin glass plate negative? With many / most manufactured silver papers that lay fairly flat this may not be a big concern, but with hand-coated papers for alternative processes...?

I have just recently been experimenting with J. Lane's dry plates (4X5) and decided to make a cyanotype - it just dawned on me that I probably shouldn't use my contact printing frame as it could crack the plate due to the pressure, and I was not sure if laying a sheet of glass over the sandwich would result in newton rings - so I just taped the plate to the paper at the edges before exposure. I have a feeling that the results were not as sharp as they could / should have been.

Any ideas?

[alexmuir]

I believe that older wooden contact frames were designed to accommodate plates, rather than film. I have a Kodak 5x4 wooden frame of that sort. I’m not sure if the frame was originally glazed, or if the plate itself was the glazing. These frames tend to be slightly larger than the dimensions of 5x4 film, which is slightly smaller all round than a 5x4 plate. The only downside for Cyanotypes, etc, is that the resulting print will have no margin. That may not be a problem, depending on how you want them to look.
Alex


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[Jim Jones]

The size and distance of the light source affects how close the negative and paper must be for perfect sharpness. The Sun was a forgiving light source for contact printing. Some large artificial light sources used close to the printing frame are certainly not.

[Randy]

Alex, I have several older printing frames - I'll dig them out and inspect them.

Jim, that makes sense - can I assume that not using the sun, but the shade, will likewise be as sharp as a distant light source? That is what I did yesterday. I didn't want to have bright mid-day sun on my glass plate (I know how hot my negatives get in the sun) so I kept my printing frame in the shade facing the blue sky - exposure was 25 minutes compared to 6-8 minutes in direct sun.

[Jim Noel]

I use the glass negatives in place of the original glass. Good contact, pressure no problem.

[koraks]

Jim, that makes sense - can I assume that not using the sun, but the shade, will likewise be as sharp as a distant light source?

Direct sunlight is for all intents and purposes highly collimated. Shade, however, is diffused. So no, you can't assume that shade will be as 'sharp' as direct sunlight. In any case, I find that you need good contact between negative and paper for optimum results. I personally use a DIY printing frame that I use with both film and glass negatives. Works fine, but the frame I constructed allows the pressure to be set with a couple of screws, so it's easy to accommodate for a thicker or thinner 'sandwich'. I also use 5mm thick glass in the frame so it doesn't break easily if the pressure is distributed a bit unevenly. I also padded the back of the frame with slightly compressible material. Excellent contact with this setup and tack sharp prints.

[Randy]

...And no problem with any newton rings? I know I got newton rings when I scanned a glass plate recently, I just assumed that could be a problem when contact printing with a printing frame.

[Nodda Duma]

Just lay the plate on the paper. Works really nice (pardon my sad, amateur attempts)




To avoid newton rings on scanning, place emulsion side against the platen and flip in post processing.

[paulbarden]

Randy,
I have limited experience printing out glass negatives, but its something I have done a few times recently. I have an old classic orange wooden contact frame (you know the ones) that I use, and I have not yet broken a glass negative used in this printing frame (and its got a lot of force behind those springs). I think if you're careful how you assemble the frame + negative + paper you will be okay - just be gentle and avoid putting too much pressure on one side of the frame. I've always made sure I position the negative so that 3/4 of it is positioned behind the larger section of the frame back, so that there's no excess pressure at the hinge, if you know what I mean.

And I have never had newton rings making prints this way.

[Randy]

Paul - I have one of those orange printing frames. Yes, it seems to apply a lot of pressure, that is what I feared. I have a glass plate that got messed up in development. I'll experiment with it to make sure it won't crack.

Jason, when I laid one of your glass plates on my cyanotype paper, the plate was not heavy enough to make uniform contact all around, the paper was slightly warped after I had coated it and it dried. I think I will have to at least lay a heaver glass over it during the exposure.