Autochromes...

[Nodda Duma]

Before spin-coating, might I suggest that you try overexposing by a stop (or double the effective ISO) if the reversal is too dark. Developed plates tend to be thin before you figure that out.

I expose my basic emulsion as an ISO 2...I would expect you are faster at least by double due to the panchromatic response. I then develop in HC-110 dil B for 5 minutes.

 

[ThePhotoChemist]

Before spin-coating, might I suggest that you try overexposing by a stop (or double the effective ISO) if the reversal is too dark. Developed plates tend to be thin before you figure that out.

I expose my basic emulsion as an ISO 2...I would expect you are faster at least by double due to the panchromatic response. I then develop in HC-110 dil B for 5 minutes.

I'm not confident that will get me anywhere... I tried something like that earlier, though granted it was a thicker emulsion. After a certain amount of exposure it seems like it hits a bit of a wall, and I'm already nuking this thing pretty hard (40 minutes). I pour these things in sets of 2's, though, so I might as well try with the other one... I'll give it a go tomorrow after work.

I think my emulsion is slower than yours (closer to ISO 1 with no screen by my measure), though i wasn't very deliberate about figuring out its speed. It's entirely possible that I have way too much sensitizing dye in it right now and it's hindering it a bit.

 

[Nodda Duma]

Gotcha. At 40 minutes you might also be suffering reciprocity failure. I'm assuming you need these long exposures due to shooting indoors? Can you set up to shoot outside? Even though you lose 2-3 stops due to the screen, your exposures shouldn't be near as long outdoors. Sunny 16 rule applies.

Hope you don't mind me tossing out ideas...seems like you're now tackling some of the non-autochrome-specific issues that emulsion makers run into as part of that learning curve. Which is good progress!

 

[ThePhotoChemist]

Gotcha. At 40 minutes you might also be suffering reciprocity failure. I'm assuming you need these long exposures due to shooting indoors? Can you set up to shoot outside? Even though you lose 2-3 stops due to the screen, your exposures shouldn't be near as long outdoors. Sunny 16 rule applies.

Hope you don't mind me tossing out ideas...seems like you're now tackling some of the non-autochrome-specific issues that emulsion makers run into as part of that learning curve. Which is good progress!

It's possible. For fun I'll do a massive exposure tonight (2 hours or so) and try to push it a bit with the developer to see if we can get a lighter positive. While it's doing that I'll start playing with spin coating (in the light).

I think it's slow because of my lighting... I only have one LED worklight illuminating the scene. By the time I get back from work it's usually dark, and right now we're lucky to have 1 day a week where it's sunny, so I've just been sticking to the worklight for consistency. Again though, it's worth a shot. I'll try it out the next time I get the chance.

Feel free to keep tossing out ideas, I gladly welcome them!

 

[Photo Engineer]

The minimum density of your positive can only be as low as the density of your screen plus fog.

PE

 

[falotico]

Autochromes required a yellow filter to be placed over the lens before the exposure was made. This implies that the emulsion was especially sensitive to blue light. The panchromatic emulsions of the first Autochromes--1906 to about 1919--were probably sensitized with the dyes ethyl red and erythrosin. The literature suggests that if these dyes were incorporated in the emulsion they did not act as efficiently as if the emulsion were bathed with the dyes shortly before exposure.

 

[ThePhotoChemist]

Autochromes required a yellow filter to be placed over the lens before the exposure was made. This implies that the emulsion was especially sensitive to blue light. The panchromatic emulsions of the first Autochromes--1906 to about 1919--were probably sensitized with the dyes ethyl red and erythrosin. The literature suggests that if these dyes were incorporated in the emulsion they did not act as efficiently as if the emulsion were bathed with the dyes shortly before exposure.

I believe you're thinking of ethyl violet, not ethyl red. Ethyl violet has a fairly poor action, especially at deeper reds (IIRC it's why people's skin looks so strange and pale). I would imagine this is why they needed that filter. Their particular emulsion also used Orthochrome T as a (green?) sensitizer, which as far as I can tell has disappeared off the face of the earth. For now I'm just using erythrosine and pinacyanol, which shouldn't require a filter.

Here's the result of a 2h15m exposure. Probably the best positive so far, but still very dark. Hmmm...

 

[Wayne]

Cool.

 

[J 3]

Amazing stuff. It's great hearing Autochrome is getting closer and closer to being replicated.

 

[falotico]

I believe you're thinking of ethyl violet, not ethyl red. Ethyl violet has a fairly poor action, especially at deeper reds (IIRC it's why people's skin looks so strange and pale). I would imagine this is why they needed that filter. Their particular emulsion also used Orthochrome T as a (green?) sensitizer, which as far as I can tell has disappeared off the face of the earth. For now I'm just using erythrosine and pinacyanol, which shouldn't require a filter.

I think your examples are wonderful and I hope you continue with your work. Ethyl violet, of course, was a popular sensitizer for photographic emulsions in the 1910's. However it is generally considered not as effective as the isocyanin dyes for sensitizing photographic emulsions.

E.J. Wall in "History of Three-Color Photography" (1925) states that ethyl red "was the first of the isocyanins" and his footnote indicates that it was introduced in 1904, in time for it to be incorporated in the first Autochromes. On page 257 Wall states "...the nitrate or sulfate of ethyl red, and which was, therefore, the corresponding salt to orthochrom T...." Ethyl red then seems chemically very closely related to Orthochrom T which you suggest was used to sensitize Autochromes.

 

[dE fENDER]

I think your examples are wonderful and I hope you continue with your work. Ethyl violet, of course, was a popular sensitizer for photographic emulsions in the 1910's. However it is generally considered not as effective as the isocyanin dyes for sensitizing photographic emulsions.

E.J. Wall in "History of Three-Color Photography" (1925) states that ethyl red "was the first of the isocyanins" and his footnote indicates that it was introduced in 1904, in time for it to be incorporated in the first Autochromes. On page 257 Wall states "...the nitrate or sulfate of ethyl red, and which was, therefore, the corresponding salt to orthochrom T...." Ethyl red then seems chemically very closely related to Orthochrom T which you suggest was used to sensitize Autochromes.

Ethyl Red (current name Ethyl Red Iodide, CAS 634-21-9)
http:://pubchem.ncbi.nlm.nih.gov/compound/5463397

Diethyl Red (current name Ethyl Red, CAS 76058-33-8) - please note, than if you buy Ethyl Red from Sigma, for example or any other vendor - you will get this incorrect compound.
http://pubchem.ncbi.nlm.nih.gov/compound/Ethyl_red

Orthochrome T (CAS 6270-81-1)
http://pubchem.ncbi.nlm.nih.gov/compound/5485634

Differences is spectra of Ethyl Red and Ortochrome T here: https://archive.org/stream/TheTheoryOfThePhotographicProcess/aa012#page/n1059/mode/2up

 

[falotico]

Ethyl Red (current name Ethyl Red Iodide, CAS 634-21-9)
http:://pubchem.ncbi.nlm.nih.gov/compound/5463397

Diethyl Red (current name Ethyl Red, CAS 76058-33-8) - please note, than if you buy Ethyl Red from Sigma, for example or any other vendor - you will get this incorrect compound.
http://pubchem.ncbi.nlm.nih.gov/compound/Ethyl_red

Orthochrome T (CAS 6270-81-1)
http://pubchem.ncbi.nlm.nih.gov/compound/5485634

From the structures that dE fENDER has posted it is seems apparent that Ethyl Red Iodide is chemically very close to Othochrome T. Wall mentions that both dyes will sensitize to wave length 6200--aproximately orange in color.

 

[ThePhotoChemist]

From the structures that dE fENDER has posted it is seems apparent that Ethyl Red Iodide is chemically very close to Othochrome T. Wall mentions that both dyes will sensitize to wave length 6200--aproximately orange in color.

That's good to know that I'm not entirely crazy. In the Lavendrine/Gandolfo book they state that Orthochrome T is used here as a green sensitizer, though all the information I could ever find about it indicated that it was more favorable as a red sensitizer. Strange that it was used in conjunction with ethyl violet in their sensitizing solution.

Here are a few new tests I have done:

With the spin coated plate, I made the mistake of spinning the plate first, and adding the emulsion to the center. The middle of the plate is nice and even, but as you can see the emulsion liked either to "run away" off the side of the plate, or congealed thickly before it could get there. I think there is merit to this, but it might make more sense to coat the plate first and spin it to clear the excess emulsion. 40 minutes, subject ~EV 5-6

The 'pour off' plate, I had decided to coat and drain the plate again collodion style, and allowed it to sit levelly to dry. I decided to see what a monumental exposure would look like - the plate was exposed overnight for 10 hours. The result is still quite dark, though you can see a bit of a gradient of thickness (thicker in the top left, thinner in the bottom right). The black streaks are due to previous emulsion coatings -- it seems the edges of the emulsion dissolve the second varnish slightly and leave behind marks. My sensitizing solutions are alcoholic, which I bet is the culprit...

In IMG_9083, I decided to see what an exposure outside would look like. This was a 2m10s exposure, subject jumping between EV13-15 (clouds kept frustrating the exposure time). I was shooting for 1m30s in sun and had to compensate a bit. It's overexposed, maybe by a stop or so, but still seemingly quite dense.

So far with these positives, all seem to share the common traits of being generally very dark, while at the same time lacking the dynamic range of how they look when processed as negatives. 'spincoat1s', attached here, has the best transmittance here, and I feel 40 minutes for this scene is probably underexposed -- perhaps I'll revisit spin coating with a longer exposure. In my previous post, IMG_9073s seems to have the best dynamic range, despite being very dark.

I'm definitely open to continued suggestions for things to try... I'm starting to get stumped...

 

[Photo Engineer]

What is the density of your undercoat, the one with the colored grains? That is the minimum base density you can get in a final image.

PE

 

[ThePhotoChemist]

What is the density of your undercoat, the one with the colored grains? That is the minimum base density you can get in a final image.

PE

Hey PE! Are you looking for a quantified value, or just a 'ballpark' comparison? If it's the latter, IMG_9083 is a great example - that big hole in the top right was caused by some tape accidentally pulling off a chunk of emulsion right before processing. The starch screen still remains beneath it.

I'm not sure if this is a decent way to quantify things, but quickly scoping things out with a spotmeter shows about 3 stops difference between the exposed screen and the *absolute* lightest part of the positive. In contrast, that negative that results from normal processing shows no difference between it's highlights and the brightness of just the bare screen. I'll see if I can track down a decent picture comparison...

 

[ThePhotoChemist]

Comparison of the negative (left) and a processed positive (right, my previous post - IMG_9083)

 

[ThePhotoChemist]

Apologies for the triple post. Behold, my new crazy plan. IT'S GENIUS.

Right after the first development and rinse, I'll re-expose the emulsion to white light through the screen side only. Assuming the emulsion is still suitably thick, the rays will propagate into the emulsion wherever the starch is not blocked by particles of silver. The reversal processing will take place in the dark, and after second development there is a final fixing step to remove remaining unexposed silver halides. Thoughts?

 

[Photo Engineer]

The first developer of a reversal process should have solvent action to build up Dmax to make clean whites in the reversal. Since the negative looks quite good, this suggests to me that there is not enough solvent action in the FD. If there was, the negative would appear to be foggy.

PE

 

[ThePhotoChemist]

The first developer of a reversal process should have solvent action to build up Dmax to make clean whites in the reversal. Since the negative looks quite good, this suggests to me that there is not enough solvent action in the FD. If there was, the negative would appear to be foggy.

PE

Thanks, that makes a ton of sense to me. This is my first developer (as outlined in the Lavendrine/Gandolfo book):

14g Metol
Sodium Sulfite 25g
2g Hydroquinone
8mL 28% Ammonia
1g KBr
1000mL H20

This differs from the original Lumiere recipe, which used a quantity of metoquinone instead of metol and hydroquinone. I shied away from this due to unavailability of metoquinone. That recipe also calls for 32mL of 22° Baume ammonia, significantly more than what I have added. The recipe I have using seemingly was formulated for some sort of Ilford FP-4 emulsion, though that's all I know about that. I'll play around with increasing the ammonia content...

 

[Photo Engineer]

Most modern formulas use Sodium Thiocyanate or DTOD. I could find the Dufay FD which might be of some use if you are interested.

Ammonia is not very good at this.

PE

 

[ThePhotoChemist]

I would really appreciate that! I managed to track this down, is that the formula you're referring to?

 

[Photo Engineer]

Thats it. See the thiocyanate there? That is a key to good reversal processing with modern emulsions. Well, really, any emulsion.

PE

 

[falotico]

DYES USED IN AUTOCHROMES

I purchased "The Lumière autochrome : history, technology, and preservation" by Bertrand Lavédrine and Jean-Paul Gandolfo. I thought Apug readers might like to see the dyes which are listed as used to manufacture the screens of Autochromes; and, also, the dyes used to sensitize the emulsion and make it panchromatic.

DYES USED TO PRODUCE SCREEN

1908 VERSION--crystal violet; tartrazine; erythrosine J; Patent Blue; solid green 3B (crystallized)

1929 VERSION--Patent Blue; erythrosine L; rose Bengal; crystal violet; solid green 3B; tartrazine

Some literature says that solid green 3B is another name for Food Green 3 (C.I. 42053). If that is true, then all these dyes except for crystal violet and rose Bengal are used for food coloring.


DYES USED TO SENSITIZE EMULSION

Orthochrome T; erythrosine; ethyl violet.

 

[ThePhotoChemist]

PE's recommended FD worked amazingly! Here are two shots I did today, at 5 and 10 minutes. No major photoshopping needed!

I've been developing in the FD for about 5 minutes @ 60F. I think I have a few more tests to dial in exposure and development times, but this is a good start. They are quite bright, despite how flat and dark they look digitally. Heating up the emulsion to coat a few more plates now...

 

[Nodda Duma]

That's awesome!