Anyone ever make Lippmann plates?

[Hologram2]

Just very briefly. This is quite surprising and exciting.

That said, we should have known better: have a look at these patents by George Sawyer:


US 4178181


US 4835090


US 5449597


US 5494787


US 5605784


US 5629143


US 5658719


US 5849468


Quite a while ago I had listed several patents related to Lippmann photography (https://holowiki.org/forum/viewtopic.php?t=5308). In the meantime, I had completely forgotten about Sawyer.

 

[ThePhotoChemist]

Just very briefly. This is quite surprising and exciting.

That said, we should have known better: have a look at these patents by George Sawyer:


US 4178181


US 4835090


US 5449597


US 5494787


US 5605784


US 5629143


US 5658719


US 5849468


Quite a while ago I had listed several patents related to Lippmann photography (https://holowiki.org/forum/viewtopic.php?t=5308). In the meantime, I had completely forgotten about Sawyer.

I should have known you had put that wiki page together! I've spent many hours going through those, especially at work when I'd rather be at home playing around with these things. Thankyou for doing that. Sawyer seems like he was an absolute monster, I wish I could have picked his brain a bit.

When it was suggested that I try out the mica, my mind actually went straight to this part of US 4178181:
"Reflecting materials suitable for application directly to the emulsion would be paint (metallic particles may be dispersed in rubber cement, as for example Venus 53" I was dangerously close to getting to the point of trying out the mercury-indium alloy that is also mentioned in the patent.

I struggled over the last couple of weeks and made countless batches of plates to replace the ones I was sharing earlier, but I kept falling short - I kept getting very yellow and unsaturated results, and I was struggling to figure out what I did wrong. I started working backwards, and ultimately determined that the hydroquinone I was adding to the emulsion to increase sensitivity seems to be to blame.

As far as I can tell, hq does work, as the first half of the plates I was sharing a couple posts ago did not need any hypering baths, but for now I am omitting it, as it was causing more issues than it was solving. I think it's worth revisiting soon, however.

I haven't quite replicated the results I shared previously, but I'm getting pretty darn close. These are bright and colorful, but still fairly contrasty, so they have a lower dynamic range and a reduced ability to render more subtle mixed colors. But it's a lot better than whatever I was getting before!

"1.5x X into Ag, No Gelatin" seemed to have best tradeoff between producing small grains and a fairly clear emulsion, while still creating polydisperse grain sizes that cut down on the contrast a bit. 'No Gelatin' here refers to the addition solution ("B") during precipitation - the gelatin remains in solution A. Omitting the gelatin here seems to produce more pure blues over variants more in line with Darran Green's original recipe, which have gelatin present in both solutions. "1.5x Ag into X, No Gelatin" produced by far the best dynamic range, but the plates were very cloudy, with tons of halation, causing very dim colors overall.

Here are my notes for the "1.5x X into Ag, No Gelatin"

Precipitation

Solution A (250mL beaker):

• 4g gelatin
• 1.5g AgNO3
• 100mL water

Solution B (100mL beaker):

• 1020mg KBr
• 7.2mL 1% KI solution
• 80mL water

1. Solution A was added to a room temp water bath with magnetic stirring to allow the gelatin to swell for a minute or two. Water bath was turned on to 40C until all the gelatin had melted
2. Temperature probe added to Solution A
3. Solution A was taken out of the heated water bath and placed in a cool water bath (cold tap water) to rapidly cool it back to room temp
4. A syringe was loaded up with Solution B
5. When the temp probe for Solution A hit 25C, it was removed from the cold water bath, and magnetic stirring set to 500RPM
   1. Going much lower than this risks the gelatin starting to set up during precipitation
6. White lights off, red safelights on
7. With the syringe tip under the surface of Solution A, slowly add in B over about 90 seconds
   1. Solution will cloud up, but should still be clear enough to see the magnetic stirbar spinning, and the temperature probe.
8. Let it mix for another minute or two, and then pour the solution in a tray and set it in a refrigerator to gel up

Washing

I like to try and let it chill just long enough so that the gelatin has set up and not too much longer, to avoid Ostwald ripening that will start ocurring. For my little fridge this is about 90 minutes.

1. Remove the tray from the fridge under red lighting
2. Cut the gelatin into small cubes with a butterknife, about 1/4" or so
3. Scoop the cubes into a 1L beaker
4. Top it up with distilled water, mix it around, and let the cubes soak for 10 minutes
5. Using a small spaghetti strainer, pour the contents of the beaker through it, allowing the cubes to collect and the excess water to drain off
6. Repeat Steps 3-5 3 more times, for 4 total washes
7. Add the cubes to a 250mL beaker

Note: I'm still seeing some crystallization on the edges of the plates, so maybe this style of washing isn't all that good, and a more traditional "noodling" would be better

Remelt & Finals

1. Preheat water bath to 34C
2. Add the beaker to the water bath with vigourous stirring (I'm trying to avoid the gelatin/AgX at the bottom and sides of the beaker from getting too hot
3. Add temperature probe and watch it like a hawk
4. The gelatin should melt between 28-31C
5. When the solution looks like all the gelatin, add in the spectral sensitizers dropwise:
   1. 2mL erythrosine (1:1000 in water)
   2. 2mL 3,3'-Diethyloxacarbocyanine iodide (1:1000 in alcohol)
   3. 0.7mL 3,3'-Diethyl-9-methylthiacarbocyanine iodide (1:1000 in alcohol)
   4. 0.75mL pinacyanol chloride (1:1000 in alcohol)
   5. Note: Darran green has suggested I add these in reverse order to potentially cut down on my contrast issues (I haven't tried this yet)
6. Add in 20mL 1% solution of chrome alum
7. Let it mix for a minute or two, and the pull it off heat. Pull from heat if it hits 34C - this time I was quick enough to keep it around 32C the whole time.

Coat the solution on glass plates. I use about 25mL per 8"x10" piece of glass, and scale down proportionally for smaller pieces. Try your best to tip the plates around and avoid using your finger to spread the emulsion, as that can cause bright spots on the plate - I still do this along the edges that the emulsion refuses to spread out on. I do this under red safelights that are as dim as possible, while still being bright enough to comfortably see what I'm doing.

Give it a while to gel up, then put them in a drying box with some airflow and let them dry for several hours (usually overnight for me).

Mica & Processing

After the plates are dry, I cut them down to size with a "Beetle Bits" glass cutter, emulsion side up.

The plates I intend to shoot over the next day or two are hypered in a 0.05% solution of ascorbic acid (100mg in 200mL water) - 2 minutes with agitation.

The plates are left in the bath while the mica is applied 1 by 1. Pull a plate from the bath and blot it between some paper towels to remove most of the extra drops. Tip a small amount of mica powder (I'm using Mehron metallic mica powder) onto the plate and massage it around with a gloved finger for 30 seconds or so. Set vertical and repeat for the rest of the plates.

Once the plates have all the mica applied, use a very soft brush and gently remove all the excess mica. Set in a drying box for 1 hour with airflow.

Expose. This batch seems to take about 12 minutes @ f/2.8 in EV12 lighting.

Development

Before development, remove the excess mica from the plate. I use a cottonball soaked in 99% isopropyl alcohol to wipe the majority of it off, and then a second dry cotton ball to dry the plate off.

I use GP-2 as a developer, but I keep the ammonium thiocyanate as a separate 3% solution so I can tweak the solvent level.

GP-2 working solution:

• 10mL GP-2 Stock
• 5mL ammonium thiocycante 3% solution
• 50mL water

Develop with agitation. It's about 2 minutes for me right now, but also my basement is pretty hot right now with the heat wave. 2-3 minutes is a good starting point.

Wash

Fix for about 1 minute with a 5% solution of hypo

Wash

With a wet cotton ball and a couple of drops of dish soap, gently rub it all over the plate and remove the remaining traces of mica powder

Wash

Fan dry.

The previous plates needed to be swelled, but they were older and I think the gelatin had hardened quite a bit, so I think there was a lot more interstitial area in between the mica particles for air-gelatin fringes to occur. All these followup plates seem to take on a lot more mica, so this hasn't been necessary.

That's all I've got at the moment, I'll update and add in some more images from this batch as I make them. I'm curious about varying the KBr:KI ratio to see if I can increase dynamic range a bit without nuking grain size. I'm also interested how much AgX I can push into this recipe before it starts having issues.

 

[Hologram2]

That looks QUITE IMPRESSIVE!


By the way, in case you have not yet visited Kremer Pigmente (www.kremer-pigmente.com). They may have some truly special kinds of iridescent particles.


Hypersensitization:


Jeff Blyth insisted on the importance of pH control regarding ascorbate hypersensitization. He pointed out it had be adjusted to around pH 5.


Processing:


As for the high contrast, could it be due to developer? I seem to remember that most of the GP-type of developers did produce very pronounced high contrast images - maybe due to the hydroquinone, metol.Hypo

When doing colloidal development I omitted the hypo step most of the time. Surprisingly, I never noticed any printout effects.

 

[ThePhotoChemist]

Oh, interesting, thanks for the suggestion! I'll definitely check them out!

I got some real cheap "holographic" powder just to try it out and see if anything interesting happened - I didn't expect much but I was curious just in case. It didn't really do too much here, I think the particle size is just way too big, so it doesn't really provide even coverage like the metallic mica does. It's definitely worth revisiting though!

Thanks for the pointer on ascorbic acid pH, I hadn't read that before. The typical amount I have always used was a 0.5% solution, but I was curious if lowering it would help reduce contrast a bit. I took a hit to the speed of the plates, but it wasn't proportional at all, maybe like a 1/4 stop at most. The 0.05% solution seemed to let the plates last a bit longer after hypering before they start taking on fog - I shot some plates that were several days old and the results were only a bit more yellow than usual, whereas the typical 0.5% solution would have produced hopelessly dim and fogged results in the same time frame.

As for GP-x developers - I don't think I shared any results here because nothing really came of it, but I goofed around with trying to modify the recipe to cut the contrast down, lowering and eventually eliminating the hydroquinone (replacing it with ascorbic acid, since phenidone alone rapidly starts to discolor). That might have helped somewhat, but I was testing them out when I was struggling with some of my most high contrast plates - so maybe revisiting those now might help take the edge off of the contrast.

My oldest plates (2014-2016 era) didn't really seem like they had a crazy high contrast, so I'm wondering what I'm doing differently now. I was definitely using a different developer back then - "pyro-carbonate", a recipe that I yoinked from some old article on Lippmann plates. I haven't messed with pyro developers much with these things recently, because the highlights tend to rapidly solarize to black, the shelflife isn't so hot, and it's a bit unecessarily toxic for something that I work with frequently. But it's definitely worth a shot to see if that helps out. I've got some pyrogallol sitting in an n-propanol solution that surprisingly hasn't turned totally black despite it being mixed several months ago, so maybe that's still good.

This was the pyro-carbonate recipe I was using, development was about 2 minutes at 20C:

• 60mL distilled water
• 2g ammonium carbonate
• 6 drops of 30% potassium bromide
• 4mL 10% solution of pyrogallol in alcohol

I was using different spectral sensitizers back then too, at first erythrosine+ethyl violet, and then later erythrosine+pinacyanol. That could have something to do with it as well. I really ought to try the current dye mix in reverse order just to finally confirm if that will help or not.

I used to omit hypo, especially when I'm just rattling out a bunch of test shots, but I started doing it with plates sensitized with hydroquinone, as they seemed to print out pretty heavily without it. I never really noticed this with plates hypered with ascorbic acid. Darran Green also warned that many of his unfixed plates that are several years old began to show signs of degredation, particularly with the plates he used with mercury - so I just do it to be safe now. I see in a lot of old texts that Lippmann practitioners advised against fixing to avoid color shifting, as well as to prevent damage to the delicate fringe pattern, but I can't really say I've noticed too much of a difference on either point. If anything I'd welcome some blueshifting now - I can't really bring them out of the basement now without applying a prism downstairs, since the ambient humidity upstairs redshifts them a bit.

Here's a shot from last night, 1h10m exposure - I think the flower moved slightly. When I initally took these plates off the leveling table and set them to dry, the gelatin hadn't quite set up yet so some poured off - I think that's where that pattern came from.

 

[Lenticular Studio]

Cool. I'm glad you're posting here too! I watched your video on autochromes and of course following your progress with the Lippmann experiments. You referenced particle size as a factor in both autochromes and Lippmann plates. It occurred to me that you might be able to refine the particles in a rock tumbler with some steel bearings. Just a thought. I need to stop giving you advice and concentrate on my own projects! Amazing progress and keep us posted!!

 

[isaac7]

I came across this on the LF photography forum. An in camera lumen print showing color With B&W paper! Well, a negative version at least. I think the color Reproduction is from a similar idea of fine grain silver refracting light. Not exactly a Lipman plate but in the same vein I think.

Paper negatives - Page 119

I make images using paper negatives, from time to time. I can't find another thread about this, and I so would like to have a thread, where I can send my students (and other interested) to see what can be done in this way... I know there's a lot of paper negatives around LF forum, but...

www.largeformatphotography.info

 

[Hologram2]

As for GP-x developers - I don't think I shared any results here because nothing really came of it, but I goofed around with trying to modify the recipe to cut the contrast down, lowering and eventually eliminating the hydroquinone (replacing it with ascorbic acid, since phenidone alone rapidly starts to discolor). That might have helped somewhat, but I was testing them out when

Many years ago I have had some success with a developer based on metol/ascorbic acid/methyl phenidone (https://holowiki.org/wiki/Silver_Processing_Formulas#MM-Collo_1):

• Metol.............................2g
• Ascorbic acid.....................7g
• Methylphenidone.................0,5g
• Potassium bromide.................3g
• Potassium carbonate..............20g
• Ammonium thiocyanate..............2g
• Distilled water...................1L

Dilute 1 : 50 or up to 1:100 (with distilled water.
On PFG-03 it produced extremely fine grains, illustrated by the yellow color of the emulsion.

I have no idea how it would perform with your emulsion. In that regard see also https://www.holographyforum.org/forum/viewtopic.php?t=6686

In the context of that discussion I participated in the making of OD-1 (https://holowiki.org/wiki/Silver_Processing_Formulas#Sergey_Vorobyov.27s_developer_-_OD-1) which is a colloidal developer, where ammonium thiocyanate is replaced by sodium thiosulfate. Unfortunately, I have no idea if this has any effect on contrast.


I now think colloidal development hugely depends on parameters like layer hardness (= "diffusion speed") and temperature.

I was struggling with some of my most high contrast plates - so maybe revisiting those now might help take the edge off of the contrast.

My oldest plates (2014-2016 era) didn't really seem like they had a crazy high contrast, so I'm wondering what I'm doing differently now. I was definitely using a different developer back then - "pyro-carbonate", a recipe that I yoinked from some old article on Lippmann plates. I haven't messed with pyro developers much with these things recently, because the highlights tend to rapidly solarize to black, the shelflife isn't so hot, and it's a bit unecessarily toxic for something that I work with frequently. But it's definitely worth a shot to see if that helps out. I've got some pyrogallol sitting in an n-propanol solution that surprisingly hasn't turned totally black despite it being mixed several months ago, so maybe that's still good.

This was the pyro-carbonate recipe I was using, development was about 2 minutes at 20C:

• 60mL distilled water
• 2g ammonium carbonate
• 6 drops of 30% potassium bromide
• 4mL 10% solution of pyrogallol in alcohol

I wonder if you could replace pyrogallol with pyrocatechol . There used to be a successful developer called CW-C2:


PART A
20 g Catechol
10 g Ascorbic Acid
10 g Sodium Sulfite
50 g Urea
One litre water


PART B
60 g Sodium Carbonate
One litre water


Mix equal parts together before use.


It is a very powerful developer, aimed originally at the Agfa materials. So I guess it would undoubtedly require some serious fine-tuning.

I used to omit hypo, especially when I'm just rattling out a bunch of test shots, but I started doing it with plates sensitized with hydroquinone, as they seemed to print out pretty heavily without it. I never really noticed this with plates hypered with ascorbic acid. Darran Green also warned that many of his unfixed plates that are several years old began to show signs of degredation, particularly with the plates he used with mercury - so I just do it to be safe now. I see in a lot of old texts that Lippmann practitioners advised against fixing to avoid color shifting, as well as to prevent damage to the delicate fringe pattern, but I can't really say I've noticed too much of a difference on either point. If anything I'd welcome some blueshifting now - I can't really bring them out of the basement now without applying a prism downstairs, since the ambient humidity upstairs redshifts them a bit.

In that context I wonder if you ever tried to dry your layers "à la DCG" (essentially using alcohol [isopropyl, ethanol, methanol] for dehydration: inserting the wet plates - right after the final water wash - into the alcohol). After a short period of time, the plates are removed and exposed to a stream of hot air. I figured that might become interesting when dealing with white (broadband) images.

Here's a shot from last night, 1h10m exposure - I think the flower moved slightly. When I initally took these plates off the leveling table and set them to dry, the gelatin hadn't quite set up yet so some poured off - I think that's where that pattern came from.
View attachment 401611

Gorgeous, I particularly like its dynamic "movement".

 

[ThePhotoChemist]

Cool. I'm glad you're posting here too! I watched your video on autochromes and of course following your progress with the Lippmann experiments. You referenced particle size as a factor in both autochromes and Lippmann plates. It occurred to me that you might be able to refine the particles in a rock tumbler with some steel bearings. Just a thought. I need to stop giving you advice and concentrate on my own projects! Amazing progress and keep us posted!!

There's some confusion here that I am no doubt to blame for - a lot of times I use the term "grain" without really differentiating what I'm talking about specifically, but I'll do my best to untangle that a bit.

Autochrome Starch Grains - these are the big old particles of potato that get dyed different colors in the process to filter the light before hit hits the emulsion.

Silver Halide Grains (AgX) - these are the light sensitive crystals suspended in the gelatin emulsion, used by both processes.

And now we've got mica particles in the Lippmann process to deal with here, further muddying things a bit.

For Lippmann plates, the AgX grains have to be really really really small - you're essentially taking a black and white picture of the scene with such an insanely high resolution that you're able to record the standing waves of colored light, so the particles have to be quite a bit smaller than the light waves themselves to record them well. That's why the exposures are so obscenely long with these things as well, the AgX grains are smaller targets for the photons to hit.

When I talk about autochrome grain size, the starch grains are 'like a billion' times bigger than the AgX. Sorting the starch size just increases the effective resolution of the plate, but even the smallest particle sizes that the Lumières used are still visible to the naked eye, if your eyesight is good at least. The AgX still needs to be smaller than the potato starch in this case, but there's practically no way anyone at home is going to be able to make AgX grains anywhere near big enough for that to be a concern, so you can comfortably go nuts with more traditional b&w emulsion recipes.

There isn't really a good way to tumble either of these, although I did try with the autochrome starch years ago with some poor results. That was more to see if I could mix up the colors better though. Right now for autochrome starch size selection I mix up a few hefty scoops of raw starch, put it in a 5 gallon bucket full of water, and mix it around real good for a couple minutes until the starch is all suspended. Then I wait for about 30 minutes - the larger particles quickly settle to the bottom of the water, while the smaller ones stay in suspension in the water. You can then dump the water into a second bucket and let it all settle out - I believe this is called "levigation", and is how the Lumières sorted their starch too.
In regards to Lippmann AgX grain sizes, since we're working sub-wavelength-of-light sized AgX grains, we try to control the size in a few different ways while we're cooking up the emulsion, mostly through keeping the solution as cool as possible and keeping the total amounts of silver and halide salts low.

I did do some levigation on a smaller scale with the "Let's Resin" brand mica - I mixed up a bottle of the stuff in a 500mL beaker full of alcohol, and then let it settle for 2 minutes before decanting the alcohol into a second beaker and letting it all fully settle out. It definitely worked, the mica was much more smooth than the raw stuff, and the reflection is a bit cleaner, but I don't think I noticed much of a difference in overall results. I'm using "Mehron" brand metallic mica now - the particle size is about on par with the levigated "Let's Resin" stuff, and it seems like it wipes off a lot easier pre-development. Maybe levigating the Mehron mica might produce even better results - I'll have to look into that.

I came across this on the LF photography forum. An in camera lumen print showing color With B&W paper! Well, a negative version at least. I think the color Reproduction is from a similar idea of fine grain silver refracting light. Not exactly a Lipman plate but in the same vein I think.

Paper negatives - Page 119

I make images using paper negatives, from time to time. I can't find another thread about this, and I so would like to have a thread, where I can send my students (and other interested) to see what can be done in this way... I know there's a lot of paper negatives around LF forum, but...

www.largeformatphotography.info

Lumen prints are really cool! I believe you're right, it's similar, but different, and I'll admit I'm not smart enough to really get any more detailed than that. The colors in a Lippmann plate blueshift when you view them at steeper angles, but Lumen prints seem to show the same colors at whatever angle you're looking at them. I think lumens bear a pretty strong similarity to some of the earliest color pictures we still have, made by Edmond Becquerel in the 1840s. His color plates suffered from the same issues as modern lumens - you can't really "fix" them without destroying the colors, and viewing them will slowly cause them to fade.

Many years ago I have had some success with a developer based on metol/ascorbic acid/methyl phenidone (https://holowiki.org/wiki/Silver_Processing_Formulas#MM-Collo_1):

• Metol.............................2g
• Ascorbic acid.....................7g
• Methylphenidone.................0,5g
• Potassium bromide.................3g
• Potassium carbonate..............20g
• Ammonium thiocyanate..............2g
• Distilled water...................1L

Dilute 1 : 50 or up to 1:100 (with distilled water.
On PFG-03 it produced extremely fine grains, illustrated by the yellow color of the emulsion.

Oh man I like how that looks, thankyou for the suggestion. I'll be giving that a go pretty soon - 30 minute development time is nuts though, hah. Though I think the suggested development time for GP-2 is quite a bit longer than what I actually use, so maybe it won't be so bad. I think I've got everything on hand to mix up some OD-1 as well. I had eyeballed CW-C2 a few years ago but decided against it, and I don't exactly remember why. I think I felt that it might not produce fine enough grains after some reading, but I'm not sure. I'd have to pick up a few extra things to make that, so it might be a little bit until I can get around to it.

As much as I like GP-2, I think it's undoubtedly not "the best", and I have to think we're very much in the Wild West phase of this process - so I'm willing to try pretty much anything. I do worry it might be easy to write off a particular developer after some experimenting - it still takes me a good 10 shots per batch to get the GP-2 dev time/ammonium thiocyanate concentrations just right, and I'm pretty darn familiar with working with it now. I'll try to do my best to be thorough when evaluating these.

I now think colloidal development hugely depends on parameters like layer hardness (= "diffusion speed") and temperature.

It's funny you mention that... When I was mounting prisms last night, I had a "one of these things is not like the other" moment. Out of 4 copies of the same exact flower scene, 3 are nice looking, but have a strong yellow tone that makes the colors somewhat innacurate to the subject. One of them isn't like that, and is far more faithful to the colors, though it's slightly dimmer as well. I think that one may have been one that I inadvertently pre-soaked in water first before development - I had gotten a bit absent minded, and forgotten to add the GP-2 stock to the water in the tray. I was a bit confused when no image ever developed out. When I realized my mistake, after the plate had soaked for a couple minutes, I then added the GP-2 and proceeded to process the plate normally. I plan on doing some deliberate tests today to see if pre-soaking acutally has much of an effect, or if that was due to something else.

 

[Craig]

Thinking of metallic particles, perhaps visit an automotive paint/bodyshop supply. Auto paint is made of up a base with metallic and/or mica particles and then the various pigments and additives are added to make up the desired colour paint.

There are various bases with metallic particles in different sizes, depending on what the paint recipe calls for. Maybe worth a conversation to see what some of these mixing bases look like and if they are suitable for your needs?

 

[ThePhotoChemist]

Thinking of metallic particles, perhaps visit an automotive paint/bodyshop supply. Auto paint is made of up a base with metallic and/or mica particles and then the various pigments and additives are added to make up the desired colour paint.

There are various bases with metallic particles in different sizes, depending on what the paint recipe calls for. Maybe worth a conversation to see what some of these mixing bases look like and if they are suitable for your needs?

Excellent idea! Thankyou for the suggestion.

Many years ago I have had some success with a developer based on metol/ascorbic acid/methyl phenidone (https://holowiki.org/wiki/Silver_Processing_Formulas#MM-Collo_1):

• Metol.............................2g
• Ascorbic acid.....................7g
• Methylphenidone.................0,5g
• Potassium bromide.................3g
• Potassium carbonate..............20g
• Ammonium thiocyanate..............2g
• Distilled water...................1L

Dilute 1 : 50 or up to 1:100 (with distilled water.
On PFG-03 it produced extremely fine grains, illustrated by the yellow color of the emulsion.

Here are some early tests with MM-Collo-1. The results are quite interesting, and I will continue to play around with it. The colors are very pure - with GP-2 it seems like I'm always fighting some sort of "cast" or "tone" to the images, be it red, yellow, or blue, but here MM-Collo-1 seems to just develop the colors more or less the way I expect the plate to look. This is an excellent data point for me, as I wasn't exactly sure what the cause of the yellow tone was - whether it was something due to development, or the emulsion itself.

^GP-2

Same exposure. The first image was MM-Collo-1, 1:5, 10mins with agitation. Dim but pure. The second was 1:50, 30min, no agitation. Bright, but overexposed.

Overall they are a bit dimmer than GP-2, but I still need to dial in the exact exposure/dev parameters - I'm hoping I can get it fairly close. Contrast, if anything, appears to have increased with these plates - I imagine this is due to GP-2 producing a level of base fog that softens things a bit. The "negative" is indeed yellow-orange with these things.

It's able to render some very subtle coloration on the butterfly wings - particularly those blue spots. MM-Collo-1, 3:100, 30mins, no agitation.

I'm noticing some discoloration of the stock solution already - I'm guessing this does not have the best shelf-life.

Even if MM-Collo-1 doesn't pan out in the long run, I see it as an incredibly useful tool for determining the spectral response of the plates/color corrective filters.

I had a batch of plates a couple of weeks ago that had a nice dynamic range, but were overwhelmingly red/yellow. They have long since been wiped... I wish I had saved a couple to see how MM-Collo-1 would have performed with them!

 

[Hologram2]

Amazing, a ghost from the past, almost thirty years ago!

Your results seem to suggest some re-tuning. Having had another look at the formula, I wondered, what would happen if one simply omitted the KBr. That should accelerate developing action and lower contrast.