Well, I think that this thread has moved in a useful direction as well. Because, as Denise has pointed out, this may be the direction needed to prepare a modern Autochrome.
As an added point, due to the cost of Silver Nitrate, I have tried to make the process of making an emulsion as foolproof as possible so that you do not waste money. That is why I use photograde gelatin among other things, rather than food grade, as the food grade variety varies substantially all over the world. These are the little things that that others seem to consider that this approach is not really necessary, but it is there in part, to save you money. It is also there to teach you the highest level of quality. You can do anything you want.
That would be fun :cool:!
Originally Posted by dwross
The silver nitrate indeed is a cost, but doesn't every hobby cost something? People can use many thousands to just cameras and lenses...
Well, I'm always poor so I made my own silver nitrate. It's very/too easy, but I would not recommend that to anyone because of the very real dangers, if you don't know perfectly what you are doing :whistling:. (To avoid misunderstandings, I have to add that if you get your silver nitrate, like most emulsion makers do, there is nothing dangerous in emulsion making (just use decent ventilation when using recipes containing ammonia).)
Actually, what drove me to emulsion making was the fact that I simply found most of the ingredients from my Dad's place. Being a goldsmith, he gave me some silver granules, 60% nitric acid and ammonium hydroxide.
I really agree with PE on creating reliable and repeatable processes. Not only because of wasting money, but wasting time too. It can be quite discouraging when the emulsion does not work.
I have found that 100 ml of emulsion is quite a good batch size to practice with. It allows you to test it even with some loss in coating, and get a good starting point for the next emulsion without leftover emulsion. You need about 8 grams of silver nitrate for this. We did 150 ml batches first and there was always quite a bit of leftover. Well, the volume went up in washing, too.
Well, after a couple years of being here, I've returned, only to be bitten by the Autochrome bug again ... curses on all of you! :-P ... just kidding on that last part.
Anyways, I'd love to join all of you in your quest to resurrect these processes. As some of you may recall, I did some experiments a few years back, so I'd love to lend a hand in getting all of this going.
With photo products disappearing from the market left and right, it would be outstanding to see something like this re-appear!
It's great to see you back on here guru!
It is definitely a voracious bug, and I think one that will eventually lead someone to make a real screen-plate product. At present I think that getting a good panchromatic emulsion is step numero uno, and then making a screen.
And it's good to be back!
The emulsion may be priority number one, but there's no reason that it has to be designed before or after the screen-place. We have enough people working on / interested in this that both tasks could be worked on in parallel with no problem!
Reproducing an -original style- screen may very well prove to be more difficult than the emulsion. Even though it's relatively difficult to make the emulsion, we have extensive documentation and the likes of Photo Engineer to help with that. The info on the original plates (unless i've missed something) is scant and conflicting, at best.
Does anybody like the idea of co-ordinating some distributed efforts?
Well to be honest, I've got some "plans" in the works that I hope to reveal in full soon. This might sound a little cryptic, but I'll explain in (hopefully) a few days. In short though, I'll be able to spend a lot more time focusing on photography in the near future, and working on both a panchromatic emulsion and a screen are gonna be high on my personal to-do list.
For a screen, I'm more or less set on an idea that would create something resembling a Dufaycolor reseau, utilizing the original technique described by Louis Ducos du Hauron. Basically it would be a dichromate (or similar) procedure with mutliple etching steps.
If I thought that coating a screen with starch grains and subsequently filling in the interspaces with carbon black could be easily done, or rather, if I understood how the heck that was done!, I might be interested in thinking along those lines. Dying the starches and varnishing them onto a plate would be trivial, but the coating/calendaring procedure is beyond me. There are a number of other ways that one could theoretically make a random screen reseau, but none that have really struck me as practicable. I'd love to know if anyone else has some ideas on that.
In other news, I know that Denise over at the Light Farm has started messing around with panchromaticity seriously and she too is interested in reproducing the Autochrome. However, she seems to be taking something of a hiatus (or she's holed up in the lab!).
Regarding the dyes that one could use in coloring starch grains or similar, we needn't look further than the acid dyes utilized in Kodak's dye-transfer system. Just as is done with some Wratten filters, combinations of C+M, C+Y and M+Y can get us the appropriate red, green and blue filter colors, and they'd have rather good permanency. Jim Browning has published his set of dyes, and there is a large list in my dye-imbibition thread. All of these are relatively easily obtainable "articles of commerce".
On the other end of things, lately I've been identifying a vast number of spectral sensitizing dyes (here, see the latest handful of posts) that could be used in emulsions; particularly old and cheap ones.
A dichromate / etching process sounds like a great idea ... I think I can even picture in my head how that might work.
As far as creating a -random- reseau, doing it [gasp] digitally would be the best way, especially if the end goal were to be a commercial project. It would be trivial to have a computer generate a random dot pattern, normalize it to obtain the correct color balance, and print the resulting image. There's no reason that an inkjet printer can't be loaded with RGBK instead of CMYK ... This could be done on large sheets, which could then be cut down to the correct size.
I encourage you to go the inkjet route for sure, but my main concerns are permanency and resolution. They're probably not insurmountable by any means, but those are my initial thoughts. I recall that you posted a RGB reseau file in the past and I might even have it on my computer somehwere. I have to admit thought that I'm not gonna fiddle with inkjets; but like you said, this could be a collaborative effort.
I looked at the method you're talking about (in the history of color photo book) - brilliant! I can't wait to see how that comes out for you!!!
Just for fun I thought I'd post this Kodak patent for a Film with Color Filter Array, U.S.P. 6,387,577.
It's interesting that Kodak has patents from so recently that deal with making, basically, screen-plate reseaus. Of course, there is application for digital sensors (Bayer arrays), but this one in particular would be suited to film.
It's a brilliant idea and would allow the screen to be in front of the emulsion, yet allow processing like normal. As opposed to exposing through the base like a typical screen-plate.