Dry plate newbie questions

[dwross]

A note on food grade gelatin. If you do go that route, order it in bulk (i.e one big bag). Divide it among many small plastic bags, sealed tight. Keep those stored cool and dry, and then open one bag at a time. Photo grade gelatin manufacture and quality control is rigorously controlled. Food grade is controlled for bloom and safety, but the other constituents (that don't matter at all for food use but can have a big effect on emulsion making) can change from lot to lot. If you buy enough to last for a long time, you'll quickly learn its characteristics and eliminate gelatin as a capricious, and potentially confusing variable.

[daveandiputra]

Another question on Kevin Emulsion recipe, There is also a possibility that I may can't get the bromide. Reading the darkroom cook book they are restrainers and potassium iodide can be a replacement with recalculations. Any chance of doing that on dry plate?

[dwross]

Unfortunately, the answer is no. Potassium bromide (KBr) serves a different purpose in emulsions than as an ingredient in emulsion making. There are three halides practically useable in emulsions -- chloride, bromide, and iodide. Cl and Br can stand alone, or be combined. Either or both can be combined with a miniscule amount of iodide, but iodide doesn't work as a stand alone halide.

Bromide, usually with a tiny bit of iodide, is the classic dry plate recipe. Kevin leaves out the iodide and does great (maybe a tad slower) but Chris Patton uses sea water, which is sodium chloride -- table salt. If you can't get potassium bromide, you might go that way. Get a brand with no additives at all.

http://thelightfarm.com/Map/DryPlate...yPlatePart.htm

[daveandiputra]

What will be the difference if using table salt? That does sound easier
Talking about chlpride, How About ammonium chloride? Does that work? I have some from a fixer formula.

[dwross]

All things being equal, the Cl emulsion will be slower with greater contrast. You might also get a bit of peppering (spontaneously developed grain.) Chris's goal is to go as natural and close to the ocean as possible. He celebrates the slowness of the emulsion. He figures (and I agree) that there are fantastic, fast, panchromatic films commercially available. Recreating them is not his windmill. He loves the effects that come from slowness and colorblindness.

Re ammonium chloride: I don't know. My philosophy is 'give it a try' (maybe after you try sodium chloride.) Use a little less. The reacting amount of KBr to one part silver nitrate is 0.7. NH4Cl and NaCl are about 0.4. The advantage of using an ammonium version of a given halide is that's a mild silver solvent. You'll be less likely to get peppering. Ammonium chloride is the usual halide in printing-out papers, but usually with silver in excess and with an organic acid, so I can't see that you'll get funky negatives with a dry plate recipe's ingredients and proportions.

Luck and fun

[daveandiputra]

Okay one more question on the halide factor, if I did use the ammonium chloride, you suggested less should be used compared to the sodium chloride?
Still waiting for the bellows for my camera though. Hopefully I can try this soon.

[dwross]

No, sorry if I was confusing -- typo (never type before a.m. coffee!) 'Am'Cl and NaCl have about the same reacting proportions. If you're substituting into Chris's recipe, use the same. If you're substituting into Kevin's, use about a third less than for KBr.

Hope your bellows come soon!
d

[dwross]

oops. In post #13 I typo'ed (again! sheesh.) Fortunately, it's obvious, but to be accurate, "...KBr serves a different purpose in developers than as an ingredient in emulsion making."

I think I counted a half dozen typos in the internet newspapers just this morning. Do you suppose it's something contagious? are we getting lazy, or is there something to this 'brains being rewired' stuff? Don't mean this to be a topic here, but it does give one pause.

[daveandiputra]

Luckily I understand what you mean
Just read a article on the net yesterday that memories of telephone numbers is declining with the invention of mobile phone with it's phone book. I guess that also can be correlated with all the auto correct functions making us lazy to proof read before publishing?
Of course I can use the excuse of not being a native speaker of English