The reason that i would need a panchromatic emulsion is that i´m trying to reconstruct Autochrome plate process for my own project. with some research and experimentation, I have been able to remedy some obstacles regarding the pitch, potato grain, lamination & sealer assemblies. I am aware that somebody has done this before using Estar etc. medium as a film base, but i am interested using a glass negative.
Now we´re talking :0)
Originally Posted by AgX
I was thinking the same thing. But if you add green & red sensitizer to fixed grade emulsion, why cannot you use the variable grade,it already contains the blue and green..? is the contrast range too big between these sensitizers..?
I made some dry plate glass negatives once with Rollei Black Magic (RBM) emulsion. See:
RBM is available in 3 different emulsions, two graded and onevariable contrast emulsion. There is also gelatine, etc. from Black Magic for coating undergrouds, etc.
Tech info & How To, click here (also about how to modify gradation, ...).
Among others, also available at macodirect.de
What type of Safelight is suitable:
* RBM23: red or yellow green
* RBM33: red or light brown, no yellow green
I hope this helps ...
Precisely, i Have bottle of Rollei Black Magic variable contrast emulsion sitting on my freezer. The problem is that one can coat a glass plate with this variable liquid emulsion, but I would need a red sensitization into it also, that i could could use it as a viable emulsion for"Autochrome" plate. straight from the bottle, I can render the blue & green but not the red. I could sensitize the emulsion using Methyl violet (ethyl I cannot obtain) but like PE said, this would probably mess the blue & green record, IDK.
To put it simple: Variation between blue and green exposure will change the contrast of the paper. Exposing such emulsion to the Image of a coloured scene would yield unwanted contrast changes.
Adding a second sensitizer will screw it up further. Though worth a try if you are already buzy with sensitizers.
Furthermore: adding a sensitizer to an an emulsion already sensitized would lead to competitive effects between sensitizers.
Originally Posted by VesaL
Forgive me my ignorance, but why would you want/need to do this?
(This is not criticism but me wanting to learn & understand this)
BTW: if I remember correctly, in the How To document I mentioned before (see link above) there is some text about mixing emulsions & influencing contrast and gradation, If my memory serves me well.
Thanks, i will have check this passage out from the documentation.
Originally Posted by TheToadMen
As an answer to your question, why men ever wanted to go to the moon or climb on top to the mountain..? :0) to get an experience and learn. The fully ( but limited) panchromatic emulsion is needed to render the visible color spectrum, in the autochromes or modern films. I like historical processes, and like to experience myself how the pioneers of color photography have made their mark in history. As a historical and scientific perspective concerning Autochromes , people can slice hair what can be done and what not, but i just don´t want to take things for granted, like iPhone on your pocket etc.
Guess the only way is to sensitize the variable contrast emulsion and see what happens, probably will not work but hey, least we tried it :cool:
Now I get it. :p
Originally Posted by VesaL
I like the Autochrome Lumière photos from 100 years ago very much! I understand it was made with potato starch, but no one has reproduced it successfully yet.
Trying to reproduce this effect, shouldn't it also be possible to coat three blank film sheets and expose each with a different color filter (at the same scene)? Then combine the three negatives and make one print?
This is in fact in theory the same as what we still do making three digital negatives (digital color separation) for color gum printing nowadays.
I once bought three old 4x5" wooden film holders with each a different glass plate in it: red, green and blue (if I'm right, would have to check). I suppose they where used for a process like this?
(BTW: I like your motivation/attitude towards experimental photography)
As has been repeatedly explained here, use of a VC emulsion will cause problems when used in a colorful environment, as it will give variable contrast depending on color. Adding red sensitization will mess things up further.
A fixed grade emulsion OTOH is easily pan sensitized by adding either a pan sensitizing dye or a green and red sensitizer. There is another thread here that describes this type of work. But, many claim to have achieved pan sensitivity, but I have seen little evidence to prove it. Doing it in color will be proof, but doing it in B&W is not proof.
Ok, now for the dyes, you add about 50 - 100 mg of dye per mole of silver while the emulsion is melted. Hold it for about 15 minutes with stirring and the deed is done. The temp should be about 40C. These dyes can be purchased from Sands Corporation in Florida. The dyes dissolve in either water, ethanol, or similar solvents. They give that information. Expect to pay several hundred dollars per gram. These dyes are expensive.
OTOH, Holmburgers has posted a list of less expensive dyes. These might be useful.
In Germany, Honeywell sold dyes.
AND: NEVER FREEZE A LIQUID EMULSION!
Thanks PE! Your contribution to this thead really clears things out on the technical side.Rollei really should update their instructions not to suggest freezing the liquid emulsion. We´ll, it was already sitting on the fridge for 4 years, before I moved it into freezer. I thought that liquid emulsion is a gelatin based, re-melting and mixing would do the job ( just making sure not to re-freeze it again due fogging)
I have Methyl violet for the Red(dish) sensitization ( it´s not optimal I know ) and Erythrozine for the green record. In original autochromes, Jack H.Coote quoted in his book " history of colour photography" that they used Erythrozine & Tartrazine & Ethyl violet for the color sensitization.
Fixed grade emulsion already does contain sensitization for Blue, if i´m not completely off-course. Because i live in a county (Finland) where we use SI -metric system, i will have to calculate the value "mole of silver" in grams. I tried google but it will give me outlandish conversion figures. well time to search some more.:whistling:
Like PE said, rendering this in color would give hard evidence. I must try this out.