Lippmann Plate Exposure and Development Guide

The Lippmann Guide Part II - Exposure and Development

Though the list of chemicals and the following procedure might look daunting if you have never made a silver-gelatin emulsion before, those who have might be surprised to see that it's not all that different from your bog standard dry plate recipe. We're just using less "stuff", and keeping the solution a lot cooler than usual.

Cutting the Plates

If you're not planning on shooting these in 8x10, it's at this point I like to cut the plates down to the format I prefer to shoot with - 6x6. I chose this format because when commissioning prisms, I could not decide if I wanted to shoot in portait more, or landscape.

I use a BeetleBits glass cutter for this, which is well suited for work in subdued light, as you can pre-set stops in the base, free to cut to your heart's content without needing to read a ruler.

Since your plates are now panchromatic, theoretically any color safelight is equally good (or bad) to use. I still use red because it just feels wrong to use anything else when working in the darkroom. The previous directions still apply here - the plates are still astoundingly insensitive to light, so work at brightness level you are comfortable with, but only just.

The emulsion is very fragile and sensitive to touch/scratches, so it's best to be gentle and mindful of how you're handling the plates, especially if you like to stack them like I do. Wearing gloves not only helps from getting oil all over the emulsion while you're handling the plates, but it also protects your hands from smaller pieces of glass that chip off from the score.

I score the glass through the emulsion, and then snap the pieces down to size as you would normal glass. I rarely, if ever, have issues with the emulsion tearing off, except occasionally for small pieces right on the edges.

Hypersensitizing

...or "hypering" is the act of pre-treating the plates before exposure to increase sensitivity. Lippmann plates made in, well, Lippmann's day, did not typically undergo hypersensitization. I have never, not once, ever been able to achieve colors without hypersensitizing my plates, and I have no idea why. Here is a rundown of some of the methods available to do so.

Ascorbic Acid
- This is my go-to method for hypering plates. Plates that have been hypersensitized with ascorbic acid should be exposed within the next day or two, or they will start to take on fog and spoil.
- Agitate the plates in a tray of 0.5% ascorbic acid for 2 minutes
- Stuff will grow in the working solution after a couple weeks - toss it and mix it fresh if you spot anything in the bottle
Triethanolamine (TEA)
- This produces results that are virtually identical to ascorbic acid, although possibly a bit brighter and a bit more blue
- This will similarly spoil the plates, so only plan on hypering plates that will be shot over the next day or so
- This will pre-swell the plate, meaning that any post-processing swelling solution used will have to be stronger than would be used with the rest of these methods
- Agitate the plates in a tray of 1% TEA for two minutes
Formate
- Some holographers have reported success with hypersensitizing their plates with sodium formate, which apparently does not spoil or lose speed after doing so
- I have never once gotten even the slightest speed increase and I'm baffled as to what I'm doing wrong.
Hydroquinone
- Adding 50mg of hydroquinone per 100mL of emulsion can give a similar boost in speed, without the need for any sort of hypering bath
- I have had good success with air-gelatin reflection plates, but I had inconsistent results when using mica, and I haven't quite gotten to the bottom of this yet

Comparison between "Ag into X" and "X into Ag", showing reduced contrast due to more polydisperse AgX sizes

At the time of writing, I highly recommend hypering your plates with ascorbic acid, especially if this is one of your first attempts. But I encourage you to explore these options (and any more you may come across) -- perhaps you'll discover something that I missed.

The Reflector

As was described in the introduction, there are two alternatives to using mercury as the reflector - the Fresnel reflection at the air-gelatin boundary, and reflective mica powder. Right now my recommendation is to go with mica, however I will be including notes wherever necessary when something is air-gelatin specific.

If you are rolling with the air-gelatin method, there is nothing to do after the hypering bath then to set the plates on a drying rack with some gentle airflow

Applying the mica mirror

Do this all one at a time - it's okay to leave the rest of the plates sitting in the hypering bath. Wear gloves, because mica is crazy messy.

I've tried a few brands of metallic mica and it didn't seem to make too much of a difference - I use Mehron brand because it's cheap.

Pull a plate out the hypering bath, and gently dab it between a folded paper towel to remove the excess drops
Slowly tap the bottle until about a dime-sized pile of mica has been tipped onto the plate
Gently massage the pile of mica around the plate - it should readily stick to the wet gelatin
Once the plate is well-covered, massage a little more firmly to work in a few more particles - this will help produce a slightly cleaner looking reflection
Brush off the excess mica with the softest makeup brush you can find
Set vertical to dry, near some gentle airflow. Typically my plates are well dried after about one hour.

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Camera Modifications

In this step, we'll be taking our silver salt and our halide salts, and reacting them together to form the light sensitive silver-halide crystals. Since Lippmann plates are exposed "backwards", with the glass-side facing towards the lens, that means the focal plane is offset by the width of the glass. We'll have to modify the ground glass if you want to still use the focusing screen. If you're using a camera that was intended for shooting film, we'll also have to figure out how to cram a glass plate in there.

You're probably going to have to freestyle a bit, but I'll give a rundown on the cameras I've used, to hopefully give you some ideas.

Bronica EC

I picked up this camera because I wanted to shoot in 6x6 format (and I didn't want to choose between portrait or landscape when commissioning prisms), and saw that the electromechanical shutter did not use power while holding the shutter open -- this is great, because we'll be holding the shutter open a lot when making exposures.

I pulled all the guts out of the standard 120 back, and created this 3d printed insert to hold the plate against the focal plane. This is a really expensive way to make, what is essentially, a really fat single-shot plate holder, but it works. The insert isn't an exact fit, so I use a piece of foam to apply some pressure to keep it in place once the case is closed. The 61x61mm version is for if you are good at cutting glass, and the 64x64mm version is for when you are not.

The focusing screen was removed, and I plopped in some ground glass that was made from the same glass stock as I coat the Lippmann plates with, ground side facing up. I was dumb and broke the focusing screen mechanism while I was removing it, so, try not to do that.

The stock SLR the camera came with has a hard stop when focusing at infinity normally -- however, due to the focal plane offset of the plate, this means that the camera can't actually focus to infinity distances. I tried to take apart the lens to see if I could remove this hard stop, and ended up screwing it up so badly I had to give up and buy a new lens. So also, try not to do that.

Comparison between "Ag into X" and "X into Ag", showing reduced contrast due to more polydisperse AgX sizes

Mamiya RB67

Due to the long exposures involved with the process, I wanted to snag a second camera so I could expose multiple plates per exposure. I picked this up because I thought 6x7 would work well with this process. Ultimately though I wasn't able to figure out how to cram a 6x7 sized plate in the 120 film backs that came with the camera, so I still use 6x6.

The 3d printed insert is pretty minimal in comparison to the Bronica one. You also can download it here.

The stock lens has the same issue the Bronica did, where it was unable to focus past infinity. However, I was able to pick up [INSERT LENS HERE] that allows for fine adjustment of the "infinity" position, meaning I would be able to photograph landscapes and stuff if I ever decide to go outside again.

Quarter Plate Holder

It's significantly easier to shoot these with large format cameras than it is medium format, since there are no endstops preventing infinity focus, and modifying the ground glass involves pretty much just flipping it around.

I bought this cute little quarter-plate camera a few years ago, but I could never source plate holders for it (or even figure out if there was a name for whatever standard it uses). So I made my own fully 3d printed version! You can download those files here.

This plate holder is designed with the focal-plane offset built in, so you don't have to flip your glass around, but there is also a "normal" version if you want to shoot regular glass plates with it, or you like having your ground glass flipped.

4x5 & 5x7 Adapters

I don't shoot these sizes very often anymore, since in a lot of respects I'm still trying to figure out this process, and I prefer having a ton of little plates per batch to experiment with instead of like 12 big ones. Larger plates can start to become very hard to even "see" the whole thing at once, unless you build a dedicated viewer for them (which, to be fair, is a box with a $5 Fresnel lens).

Using antique plate holders was always kind of hit or miss for me, since a lot of them have warped a bit as they've aged, and no longer hold the plate quite on the focal plane. When I did shoot these sizes, I typically used "Premo" Packfilm adapters, with a 3d printed insert to hold the plate in place, which always worked really well. The packfilm adapters sometimes have a little variance in size, so you may need to tweak the sizes a bit in the design for your particular model. You can download those here.

This design coupled with the holder gives the appearance that is possibly one of the light-leakiest things I've ever worked with, but fort whatever reason I've never had any problems at all with this, though YMMV ¯\_(ツ)_/¯

Exposure

The exact exposure you'll need for your plates will vary a bit from batch to batch, especially if you haven't quite developed a "ritual" yet. Furthermore, the exact development parameters will vary a bit too. I like to remove any extra variables that I can from the equation so I can figure out the exposure/development sweet spot without blowing too many plates. So when starting a new batch, typically I'll shoot in an indoor lighting setup until I feel comfortable with the results.

The LED panels I have can get me to about EV12. At that brightness, smaller subjects such as flowers seem to take about 60 minutes @f/4 for a good exposure. This comes out to about 7 minutes exposure time on a sunny (EV15) day, all else equal.

The nice thing is, in my experience, Lippmann plates always followed a typical response to different lighting conditions - e.g. I haven't seen any reciprocity failure, even when cranking the aperture real small and sending exposure times into 10+ hours.

Since it's pretty difficult to get a truly isochromatic response (e.g. the plate will probably be more sensitive to certain ranges of color than others) a lot of the time I find it helpful to use filters from a CMY printing kit (in particular I use an old one made by Cibachrome). If your plates are really out of whack and much more sensitive to certain parts of the spectrum than others, these can really help smooth the response curve out a bit - at the cost of even longer exposures.

When you are ready to go shooting out and about, I highly recommend a gray card and digital spot meter. Lippmanns are a positive process (you can't fix them at the enlarger later, and there really aren't any good options for intensification or reduction), so getting the exposure right the first time is crucial. Additionally, Lippmann plates don't have an especially high exposure latitude, making this even more challenging. Being able to measure the light levels of your subject accurately and precisely is pretty helpful.

That being said, sunny days seem to be fairly consistent, and 90% of the time I don't even bust out the spot meter.

Another consideration you'll have to make, is adjusting the exposure based on bellows extension, if you're not using an SLR. When focusing on closer subjects, typically "large format style" lenses will need to be moved out. Since the aperture is (focal length) / (lens width), focusing on closer subjects can start to mean you're actually working with a very different aperture than whatever it says on the lens.

This site explains the different methods much more succinctly than I ever could. I've always just used method #1 and just calculated it manually.

Development

We can't use just any old developer to develop these things. For the Lippmann colors to work at all, it's essential that the developed silver grain to end up in the exact same place that the exposed silver halide grain was. As it turns out, your bog standard black and white developer starts to do some really weird stuff on a micro-crystal level. They technically do work still, at least a little bit, but they will be incredibly dim with barely any trace of color. We'll be needing to use developers from the "physical" or "solution physical" classes to get good results.

Note that no colors will be visible at all until the plate has fully dried.

GP-2

Unless you're deliberately experimenting with other developers, GP-2 is hands down the winner, and the only one I explicitly recommend using. It has a pretty reasonable shelf-life, it doesn't have any explicitly toxic chemicals (don't drink it though), and it tends to produce the best "whites" out of any developer I've tried.

Stock Solution

Phenidone, 0.2g
Hydroquinone, 5g
Sodium Sulfite, 100g
Potassium Hydroxide, 5g
Ammonium Thiocyanate, 12g
Water, 1000mL

*The "official" version calls for "methylphenidone", aka "Phenidone B". Phenidone A is way easier to source. There isn't really much of a difference in terms of quality. I think Phenidone B just lasts a little bit longer.

I personally have one modification to it - I omit the ammonium thiocyanate from the rest of the GP-2 stock, and instead keep it i a separate 3% solution. Being able to adjust the amount of silver solvent on the fly like this can be super useful, since there can be a little variance from batch to batch.

Typically I make the stock in a 500mL size rather than the full liter. It will begin to yellow after a month or so, which means it's beyond its expiration - even when shooting tons of Lippmann plates I never get through it all before I have to toss it.

Working Solution

Water, 50mL
GP-2 Stock, 10mL
3% ammonium thiocyanate, 5mL

Typically I would notate a working solution like this as "50+10+5"

The amount of silver solvent required will vary based on your crystal size - so unless you have an electron microscope, we'll only really be able to figure this out empirically. Too much solvent causes an overall muddy-gold tone to overpower everything. Too little solvent tends to produce dimmer, contrasty scenes with pure colors.

Development time can also vary. At 20C, development times can range from 90 seconds to 4 minutes. Usually 2m30s is a good starting point.

Left: 60 minute exposure, 50+10+5, 2m30s development

Right: 90 minute exposure, 50+10+3.5, 3 minute development

Reducing the solvent concentration produced more faithful colors, while taking a hit to brightness, thus requiring an increased exposure time to compensate.

Fixing

Fixing the plates has always been... weirdly contentious? Even going back to Gabriel's day. Apparently skipping fix and just letting the plate print out doesn't totally mess things up. But I grew up developing black and white film, so skipping the fixing step just feels wrong. Additionally, Darran Green has noted that his older mercurial Lippmanns that were unfixed ultimately experienced some serious degradation.

That all being said, the developed out silver particles are very small, meaning they are easily attacked by the fixer - so it's best to keep it to a minimum. Fix in a 5% solution of hypo for 60-90 seconds, and then give it a long wash.

(Mica only) Second Mica Removal

If you used the mica mirror, there is still probably a thin layer of particles that are stuck resolutely to the gelatin. These can be pretty easily removed. I wet a cotton ball with water, and then put a few drops of dish soap on it. Gently massage the plate - the mica should detach pretty easily. Just be gentle as to not scratch the gelatin.

Swelling

Swelling is ultra-important if you used the air-gelatin method, and is either less important or not even necessary with the mica method. Air-gelatin plates experience gelatin shrinkage during development, which will cause the colors to be heavily blue-shifted unless we soak some extra stuff to prevent the gelatin from collapsing all the way down. We have a few options:

Citric Acid
- This is my go-to these days. It's basically the exact same as glycerin in performance, but it's easier to measure out since it's a powder and not a super thick goop.
- Will grow stuff after a few weeks - dump it and remix if it starts to get cloudy.
- 0.5% is a good starting point
Glycerin
- This is the tried and true option that has been used for many years.
- Measuring it out is really annoying
- Toss when you start to see stuff growing
- Try 0.5% to start.
Triethanolamine (TEA)
- You might be temped to use this, since it is also used as a hypering agent. However, I'm not a huge fan - it seems to dry somewhat unevenly, with the colors blueshifting or redshifting. I think the holography guys get around this by squeegeeing the plate before setting it on the drying rack, but I've never tried this.
Sorbitol
- I have heard this can be used, however, I have not myself tried this.

Regardless of your choice in swelling agent, they all work more or less the same - the higher the % concentration, the more redshift you achieve. The goal here is to bridge the gap between the amount of shrinkage from development, and where the plate naturally rests in your local ambient humidity. In my experience there isn't really a great way to remove this stuff from the emulsion once its dried, so you might have to shoot a couple plates while tweaking the concentration.

In my opinion, this is the step that makes-or-breaks air-gelatin plates. It helps to keep a good log of additions/dilutions of the swelling solution. I tend to still be a bit conservative with the concentration. If the plate is just a bit too blue, you can always run the shower on hot for a few minutes to get the room nice and humid -- this lets the plate slowly redshift, until they look just about right. Then you can slap a prism on there and seal it in like that forever. If you overswell the plate, there's a little less wiggle-room to work with. You can always let it sit on a heater or something, I guess.

Getting the swelling exactly right is much less of a concern with mica. Depending on the hardness if the gelatin, it may not need it at all. Most of your color is coming from the contact area under the mica particles, and these are "metallic fringes" that do not require swelling. However, if there is a significant amount of gaps between the particles, air-gelatin fringes will form here - and those will throw off your colors unless properly swelled. It's a bit difficult to see because it's very subtle, but the two sets of fringes catch the light at ever so slightly different angles.

If your gelatin is a bit stickier, you might not even need to swell at all, if pretty much all the gaps are filled. If this is your first mica plate, I'd skip this step and just see what happens.

To swell the plate, just rock it in a tray of your swelling solution for about 2 minutes, and then transfer the plate directly onto a drying rack. If you have some gentle airflow, dry time is typically about 20 minutes.

The difference between a properly swelled plate, vs. an underswelled (blueshifted) plate