How to make a positive dry plate? (liquid emulsion)

Last month I start being obsessed in making calotypes. It's been a while I became obsessed in taking photographs and making prints in the most old, traditional and often weird way possible.

At the same time I didn't stopped printing my bw prints and occasionally some bromoil. I use only liquid emulsion (generally on paper) and it's very rare for me to print on modern factory-made papers. Anyway, I was running out of emulsion... So I decided to prepare some bromide emulsion myself. I did it once in Denmark with Emil Schildt and worked well. I did it again now and worked still perfectly. I just followed instructions for the only unwashed bromide emulsion described in the "Silver Gelatin" book (the bible of liquid photographic emulsions). This time I attempted to prepare also some "gaslight" silver chloride paper too, but results were odd. I did not investigate on that because I'm happy with the bromide emulsion. Key factors are gelatin type/quality and temperatures. The homemade bromide emulsion is great for regular b+w printing, b+w toning, and even bromoil.

Yesterday I had this idea of trying to make a dry-plate... I made wooden plate holder for a 4x5" camera and I couldn't wait too long to try it with a "real" plate. With great surprise it worked very good on ordinary glass. No noticeable frilling on the edges, just a couple of bubbles. And no subbing layer! All kinds of commercial emulsions always lifted from the plate when placed in the developing bath. The exposed and developed plate is now drying and looks soooo nice. It's a bit slow though. Under the enlarger the emulsion took 5 minutes at F4 to deliver a good, contrasty picture. Used as dry plate, with 7' at F8 I had a badly underexposed image (indoor lighting, it was evening time). Anyway I've rated the emulsion ISO 3-5 (like my latest calotypes), which is ok enough to photograph people during daytime.

It would be really nice to make positive plates. I know that collodion wet plates consist essentially of an underexposed/underdeveloped negative that looks like a positive when placed over a dark/black surface. While daguerrotypes were real positives, right? And how would it work for a dry plate made out from a silver bromide gelatin? Is there any process for inverting a bw print that will work in my case?

Hi Fulvio - I don't know about reverse-processing (the chemistry might lift the emulsion?), but have you considered projecting an existing negative onto one of your plates? Might be interesting!

regards,
Neil.

The chemicals for reversal processing are pretty nasty, and some of them have a tendency to soften up the emulsion significantly. I doubt that it would work, but you never know.

The methods used for ambrotypes would probably be more successful.

So far I found this recipe suitable for print reversal:

1) Develop in standard developer
2) Place in acid stop bath
3) Wash
4) Bleach in a non-rehalogenizing bleach
5) Wash
6) Redevelop with same developer
7) Stop
8) Fix

The bleach required is made of either potassium permanganate or potassium dichromate in a weak sulfuric acid solution

And I know how nasty the dichromate is... (I use that for Bromoil and I always very afraid of handling that chemical...)

What do you think of it? I have already the dichromate, I don't have the sulfuric acid...

I guess the same procedure for wet plates won't work... But since the wet plate trick is to have a very weak image that appears to be a positive when positioned on a dark surface, why one couldn't do the same with a bromide emulsion? Sometimes I had that effect by chance with badly underexposed/underdeveloped film... How to make that accident repeatable?

As for the idea of exposing the plate under the enlarger: clever, but no fun

The underexpose + black backing trick should work. It's going to require lots of experimentation though. Thinking about it, why not make 3 or 4 exposures on one plate by removing the darkslide partway, exposing, moving it again, exposing again, etc. That'd get you a series of steps of exposure, each one stop more than the previous. (You'll save plates too).


As to reversal, I've used dichromate & ferricyanide bleaches. The dichromate is nasty, though once its in solution its much easier to work with as there is no dust issue. The ferricyanide bleach tends to soften the emulsion much more.

You could also just contact print the plates.

You should be able to make a faux ambrotype by exposing slightly less than normal and underdevelping the negative. When dry, place on a piece of black velvet and it should reverse to a positive.

Thanks for the advices...

Right now I'm having other problems with my homemade emulsion, though:

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it worked nicely the first days, then I had an apparent decrease of speed and finally a chemical fogging...

Anyway, how about using the same developer for collodion wet plates? I'm not sure if this will work... the developer for "positive" plates consist of a solution of ferrous sulfate, slightly acidified with acetic acid and some alcohol...

I partially gave up the idea of making positive dry plates. It works, but it's very odd. If one wants to make a positive plate from a negative plate, dry plate negatives are usually too contrasty to make a decent print. Sometimes is possible, though, but the negative must be very good then. Very often the positive image on glass will look odd, I mean it won't have the feeling of an in camera plate for some reason...

One can print a positive use a film negative instead (enlarged or by contact), and print on the plate like printing on a piece of photographic paper then. I tried that too, it's fascinating, but doesn't have the same feeling of a plate at all. Another way is to take the picture with a glass negative and make a digital negative out of it and print that by contact. Scanning a dry plate negative reveals a lot more details, which would be normally too hard to print on another plate. Results can be satisfactory, but addings steps takes time and money, plus it's not exactly what I were looking for.

I'd recommend to those interested in dry plates to varnish the glass before coating. I found out that also commercial emulsions work very well on glass as long as you varnish the glass first. The glass must be VERY clean before coating anything on it. Also, you can sand a little the edges of the glass to improve adherence. Then you can choose either to spray some varnish on it or coat with subbing solution made with very little gelatin (5 g / Liter) and chrome alum (combinations of varnish and subbing gelatin layer are possible). It really works.

Perhaps in new year I will start making some real wet plate positive. Maybe it's less hard than one can imagine, who knows...

rockland colloid sells a tintype kit that reverses the negative.
its for making silver gelatin tintypes as well as silver gelatin glas ( like ambrotypes)
it uses a proprietary developer which is like a weak bath of dektol, fixer and thiocyanate bleach
but its trickier than that ... there are a handful of threads here on apug about this finicky process.
ive made a handful of these tin and glass images and i am currently trying to concoct my own revesal developer.
street photographers in around 1900-ww1 used this process, but unfortunately very few
of the developer recipes have surfaced.

(there was a url link here which no longer exists)
(there was a url link here which no longer exists)