Best contrast for emulsion coating black aluminum (a.k.a. emulsion-based tintypes)?

Hey folks,

I am in the process of coating black anodize aluminum plates for someone who wanted to try making tintypes with emulsion instead of collodion. I sort of have to figure out what to do to make the emulsion stick -- which I'm doing -- but I'm not sure about which emulsion will give the best final results: My normal, regular contrast (gamma about 0.7) emulsion, or a faster, high contrast (gamma about 1.5) emulsion?

What are your thoughts? The best answer would be "test" but I have a limited amount of black aluminum plates (as in none to spare) and sort of just need to make a choice and go with it.

-Jason

Hello Jason,
By emulsion I'm assuming you mean a gelatin emulsion. First on the area of contrast, unfortunately tintype positives don't work like more conventional paper / film products. A tintype is exposed and developed as if you were attempting to produce a very weak negative. If it were viewed without the back backing it would look like a really transparent negative with very low contrast and no areas of high density. When placed against a black background the darkest areas of the negative (a dark grey) are lighter than the black and so appear as if they are a relatively while. Likewise the transparent areas appear black. So what governs how much contrast a tintype has is 1) how black the background is 2) how much light the darkest / most exposed areas can be made to reflect. This is a rather tricky balance that is hard to get right. If you develop the emulsion too much you'll get both negative and positive areas on the same image (the darker image areas will be a positive and the lighter image area will render as a negative). Because of how different you expose / develop the image I'm not sure you can say which emulsion would be better. BTW tintypes have to be varnished as well because the silver layer is so thin and delicate and susceptible to oxidation.

Rockland sells a gelatin emulsion kit with developer that goes on metal plates where they have worked out the exposure times. It however coats onto enameled plates (called trophy steel) which brings up the second point. Hard anodized aluminum is a porous layer of aluminum oxide with a dye soaked into the pores (black in this case). The problem may be (I don't know) would there be enough aluminum in the mix to mess up the photo-chemistry. It's common for any metal ions to do so but I'm not sure if you'd see the effect with anodized aluminum. If so you'd have to have some kind of barrier coating between the emulsion and plate.

As for how to get it to stick and possibly dealing with the metal problem, if it were me I'd try transparent workable fixative (like Krylon Fixatif (KO1306). I don't know if it'd work, and I'd be real careful in case the stuff might run off and mess up a whole batch of emulsion, but it's what I'd try.

Anyhow that's all I know. Hope some part of that helps in some way.

hi nodda duma
read the thread where
DonF describes his developer
and his treatment of the plates
he is using NON ROCKLAND plates
and describes the work it took to get the
emulsion to stick to american trophy plates
i can't speak to the gamma / contrast
i know that the rockand developer
will reverse all the bottled emulsions
that they make, i make and others like foma makes ..

looks like from your gallery posts you figured it out though

john

Thanks for responding. My emulsion coated just fine. I haven’t used Rockland and wouldn’t want to. Everyone I’ve seen talk about using it tells me it’s a real pain in the butt to use. I think their developer kit is real close to what DonF hashed out.

My tintypes in the gallery were developed with a formula that Nick Brandredth is working on. It came out nice, but needs tweaking. The fellow I coated the plates for that prompted me to post has reported good results with HC-110

I haven’t tried DonF’s formula yet but I want to. Modern Collodion has some of my costed tintypes now for testing.

Nodda Duma said:

Everyone I’ve seen talk about using it tells me it’s a real pain in the butt to use.

Click to expand...

i think some of the problem people have with it is that some folks don't let it ripen in the tray, the kits don't sell so they might get
the small kit with old developer in it so it doesn't work well ( and they don't call rockland to get it replaced )
or they don't use distilled water and they have iron and other contaminants in their developer
or they either coat their plate with too much emulsion or too little emulsion ... there's a sweet spot ...
not only that, the exposure has to be sort of right on like shooting chromes over and underexposed doesn't really
come out like with a bunch of slop / wiggle room like an under exposed or over exposed paper negative...
there was a user here and/or the large format site named calamity jane who was hoping to shoot these sorts of plates for
wild west reenactment shows back in the day and she wrote of all sorts of troubles she had and all the wet platers who wanted
to illegitmatize this process hopped on her thread and others to make it seem like it wasn't authentic and no wonder why it didn't work ...
turned out her developer was old and needed to be replaced .. rockland sent her new developer and the plates worked out great ..
IDK i think because the developer you are using it doesn't develop in a monobath and then bleach bleach back the darks, but instead
does something different makes it so the exposures dont' have to be perfect, which might make them easier ...
looking forward to trying your developer when it's released !

john