This post is in answer to a question from Esmee (check out her work via https://www.eamy.nl/). Since others might somehow benefit from it as well, I might as well just put it up for everyone to see. So here’s a little shopping list of what’s needed to get started with carbon transfer using DAS sensitizer.
First of all, there are many ways to skin a cat, as the saying goes. A horrible saying, if you think about it. And I love cats! But in a way it’s appropriate because one could of course use parts of the cat (particularly its skin) to make gelatin out of. No, please – don’t. What I’m getting at is that this is just an example of a list of materials for carbon transfer. There are many alternatives for most of the materials and ingredients. I’d encourage anyone to experiment – lots.
One more caveat: I’m only going to focus on DAS as a sensitizer, ignoring the alternatives, including dichromate (kind of yuck/dangerous, and banned in Europe to begin with), ferric salts and other azo-salts (e.g. 22LZ). DAS carbon is by now an established practice and frankly the most sensible/sane way of starting out at this point, at least in my opinion. Even though dichromate does have some benefits – again, just my opinion.
To give some structure to this post, let’s try and group things according to the main material-making phases of the carbon transfer process. Which looks more or less like this:
Note that these are not all the steps in making a carbon print, but only the steps where materials enter the workflow. Let’s see what kind of materials we might have to bring to the table.
Can’t be bothered with the lengthy explanations? Click here to scoot over to the shopping list.
Carbon tissue production
Carbon tissue is essentially pigment suspended in a gelatin matrix and some stuff that makes it possible to handle the material in a carbon workflow. The tissue is produced by pouring a molten gelatin emulsion (‘glop’) onto a suitable support and then allowing that to dry. So let’s start at the top:
Pigment
This probably remains my favorite part of the process, because you get to rummage through all the different colors available!
Pigment is a bit of a misnomer, because what you really typically add is a colorant. Typically used colorants are Indian ink, watercolor, gouache or acrylic paints. The most important ingredient of this colorant will be the pigment, but there will be other stuff present that ensures the pigment mixes nicely with water, doesn’t grow mold, doesn’t separate out when left to stand, etc. If you use ink or paint, don’t worry (too much) about these additives. Pick any nice color you like for your printmaking.
Some carbon practitioners use dry/powdered pigments and process these themselves by dispersing them. This is a bit of a story unto itself, and one that I have written about a few times in the past (see e.g. here and here).
In-between solutions that combine the best of both worlds of dry pigments (i.e. low cost, ultimate control over ingredients, choice) and ready-made colorants like paint (convenience, dispersion quality) are so-called color pastes (e.g. Kremer Pigmente or The Wet Print). These are essentially super-concentrated paints that give lots of bang for your buck/Euro. Another option worthy of mention are Kremer’s innovative XSL pigments, which are tiny pellets of nearly pure pigment that disperse readily if you add them to water. Pure magic – but the choice of colors is currently somewhat limited, still.
Colorants that don’t work are dye-based colors (e.g. ‘Ecoline’), since the dyes will just dissolve out of the gelatin matrix and stain the paper of the print. In addition, oil-based paints will not work since they will not mix with the water-based gelatin emulsion. Some paints that seem suitable at first glance turn out not to work well because of these reasons; they may contain additional dyes (I once found a very nice purple-black India ink that turned out to be black with a purple dye…) or oily ingredients (acrylic paints may give trouble because of this).
When starting out with B&W printing, a decent Indian ink (e.g. Talens) is really the way to go. If you want to experiment with color, you can’t go wrong with watercolor paints from a decent brand (Winsor & Newton, Daniel Smith, Van Gogh/Talens and many others). They’re the most expensive per gram of pigment, but easy to acquire and work with. Can be mixed with each other and with Indian ink if desired.
Gelatin
Gelatin is an insanely complex subject, but in the end, most of it will work. There are two main types: type A, from bovine sources, and type B, from porcine material (typically pig skin). Either will work, but Type A bovine is argued by some to be a better choice.
Gelatins are usually rated according to their bloom strength, which is a measure of how firm (gelatinous) a molten gelatin/water mixture is when it’s allowed to cool down and set. For carbon transfer, moderately high bloom gelatins (250-300 bloom) tend to work well.
The main determinant of the price of gelatin appears to be its purity, which correlates to the color of the gelatin. Carbon transfer tends to involve fairly thin layers of gelatin and I’ve never found the yellow/tan color of somewhat lower grade gelatins to be a problem. But if it bothers you, look for a higher-end (more expensive) gelatin that’s more colorless.
I’ve tried several gelatins myself and frankly, they all worked. There are differences, for sure, so I’d recommend to pick a good gelatin and then stick with it (at least for a while). Gelatins I’ve had good experiences with include 250-bloom bovine food-grade gelatin from NaturalSpices and a porcine 280-bloom Gelita ‘type 2’ photo-gelatin retailed (among others) by GMW. Their ‘type 1’ bovine gelatin is apparently even more suited for carbon tissue, although I can attest to the type 2 working very well indeed.
The main drawback of the porcine gelatins in my opinion is their smell – the bovine gelatins smell decidedly less of dead, decaying animal. This is only apparent in very specific parts of the printing process, however. According to expert carbon printer Kees Brandenburg, carbon tissue made from porcine gelatins tend to fog over (much) time. I wouldn’t know; I tend to use up my tissues within a few weeks anyway.
Plasticizers and humectants
Sugar is another main ingredient of carbon tissue. I use plain white crystal sugar – the same kind you’d use for baking muffins. Honey will also be fine. But crystal sugar is cheap, proven, easily available and easy to work with. Sugar helps to keep the tissue pliable when it has dried, and it also helps the tissue to easily absorb water when printing time comes. I usually add sugar to 50% of the amount of gelatin, so a glop recipe with 100g gelatin I would add 50g sugar to.
Glycerin is sometimes used especially in dry climates, and also helps to keep the dry tissue supple. I’ve used it for a while and it worked fine. Don’t add too much; maybe a few milliliters to a liter of glop. I use an 86% glycerin from a local drugstore chain sold for cosmetics purposes. But it’s not really necessary to add any glycerin in our Western-European climate.
Sensitizer: DAS
DAS, the carbon printers’ pet name for diazostilbene (CAS 2718-90-3) is what makes carbon tissue sensitive to UV light. It’s the modern and more benign alternative to dichromate, and has several advantages. One of which is that it can be added to the glop when making tissue, so the tissue is ready to be used as soon as it’s dry – it does not have to be sensitized, dried and then used quickly before it deteriorates. Because DAS tissue is also stable over time and will remain usable for many years under decent storage conditions.
One of the drawbacks of DAS is that it’s somewhat difficult to obtain, because it has very few applications. It is presently sold by a handful of suppliers in China, but also in the US (Secant Chemicals) and Europe (Phototypie.fr, Antonides, Disactis, ChemicalPoint), but it’s often out of stock and supply seems intermittent. It’s also fairly expensive in relation to the other ingredients. It’s the price we pay for not having to handle a more dangerous chemical like dichromate.
Substrate
Now the tissue only needs something that holds it together: a suitable substrate to pour the glop on. Many materials work for this; I’ve used different types of paper and polymer films in the past and by and large, they work. But the best option hands down is a material called Yupo and that is fortunately now also fairly easily available in Europe. It’s a synthetic material (‘plastic’), it’s dimensionally stable, reusable and the gelatin tissue poured onto it adheres very well to it. Look no further, really.
Well, Kees Brandenburg argues that there’s one thing even better than Yupo: Agfa Synaps. As I understand, it’s very similar to Yupo, but it appears to be only available through distributors of wholesale printing materials. I have yet to try it, but certainly will as soon as my big pack of Yupo runs out. Which will not be anytime soon, I’m afraid. In any case, I’m not sure how anything could significantly beat Yupo for carbon tissue making, since this already works really, really well.
Space and equipment
The making of the glop can be done in just about any space and in daylight conditions – until the moment when the DAS is added to it. I generally do this after the lengthy process of degassing the glop, which takes several hours (but you don’t have to monitor it closely).
Once the glop is light-sensitive, no UV light must be in the working area. This means daylight has to be shut out, but (white) artificial light is mostly OK. White LED, (UV-shielded) halogen or incandescent interior bulbs are fine. Watch out with fluorescent (CFL’s and tube lights) as this can emit significant UV radiation. The dry DAS powder should also be stored in absolute darkness.
For drying the (UV-sensitive) tissues, a dark space is best. It’s nice to have some kind of airflow going on to accelerate drying. Some kind of fan blowing air across the drying space is a good idea.
For melting the gelatin and keeping the glop warm during the degassing period, it’s nice to have some kind of hot plate or a sous vide cooker. Either works fine, and I use them alternatingly. A temperature between 38C and 50C is good – and it doesn’t seem to be very critical. When degassing the glop, bubbles will rise all the time and these can be ‘popped’ by spraying the surface of the glop with some ethanol (fuel ethanol works OK) from a spray bottle. Stir gently with a glass stirring rod.
For pouring the tissues, make sure to have a flat and (perfectly) level surface to work on. A squeegee is good to have around; I usually mist the backside of the Yupo sheets with a spray bottle, stick them to the worktop and then squeegee the excess water from underneath the sheets. This prevents the sheets from buckling under the heat of the gelatin glop when it’s poured on.
A comb is also nice to spread the gelatin with. And you’ll need some (glass) beakers or jars (I’ve used peanut butter or olive jars many times), and a precision scale. The kind of scales you can pick up from AliExpress or Amazon etc. for ‘jewelry’ work fine.
For exposing the tissues, you’ll need a contact frame. If your tissues are nice and supple, even a heavy sheet of glass will work – but a frame is really much nicer. A spring-back frame will work fine for prints up to 8×10″. For larger prints, a vacuum frame is generally recommended.
You also need an exposure unit. DAS carbon is the only process I’m aware of that won’t work well with cheap 400nm LEDs. You’ll need a light source that emits a significant power at lower wavelengths around 365nm or so. This can be a LED floodlight (make sure to get the 365nm type!!) of at least 100W, but a bank of UV-BL tubes, a big (>300W, preferably 1000W or so) metal-halide light (‘plate burner’) or an array of 365nm LED strips will also work. In a pinch, an old face tanner may be used, but exposure times will be looooong.
Wear sunglasses when exposing your prints. UV at 365nm is not necessarily super dangerous, but you’ve only got one pair of eyes to play with.
You need some kind of hot water supply for developing prints, cleaning utensils etc. I use a water cooker, but any other arrangement is also fine as long as it gives water of >40C.
Temporary support preparation
In a DAS-carbon workflow, you typically develop the print onto a temporary support and only when that’s done, transfer it to its final (paper) support. This is because we need to clear a sensitizer stain from the print and we can’t do that if the print is already on paper. So the temporary support is really just a sheet that the gelatin image adheres to for a while, but image needs to release from it when it moves over to the final paper support.
Temporary support substrate
For the temporary support, many types of polymer film are usable, notably PVC, polypropene or polyethylene films. For something seemingly simple, these films are really a massive maze to get lost in and before you know it, you’re digging deep into documentation from major chemical manufacturers like Dow etc.
I guess there are two (sane) ways of going about finding a suitable temporary support substrate: (1) purchase a material that’s know to work, or (2) try whatever you can get your hands on and stick with whatever works for you.
If you’re going to do (1), the best advice I could give is to buy the polymer film from Calvin Grier which really isn’t all that expensive if you keep in mind that the material is reusable. I also have good experiences with Esselte Dataline laser printer film – it works reliably for me, in any case. The drawback is that it only comes in A4 size, which is barely large enough for 8×10″ prints – and not quite large enough if you want to do something with pin registration.
In case of (2), it’s just a matter of buying stuff and experimenting. From a local arts supply store I bought sheets of what they called “montage film” and “paterno plate”. Both worked. I also bought some miscellaneous plastic sheets, which as far as I can currently tell also work just fine. I even tried the clear wrapping plastic they use for gifts and flowers – and sure enough, it worked. Its main drawback is that it’s so thin and flimsy. Ideally, you’re looking for something with a thickness of 0.1mm to 0.25mm or so.
Even glass will work for a temporary support. But it’s heavy, fragile and inflexible, so I don’t recommend it.
The only thing I tried and that really didn’t work for a temporary support was a silicon coated polyethylene film. Literally nothing will stick to it – which makes it useful for storing prints etc. So avoid anything silicon coated for temporary support substrates.
Subbing materials
Some carbon printers have good experiences developing their images onto untreated plastic sheets. In my experience, this doesn’t work, and the sheets need a pre-treatment that allows the gelatin to stick better. This pre-treatment is common in the film-manufacturing industry and the thin layer deposited on the plastic film is often referred to as a ‘subbing layer’.
The prime choice for this subbing material is…wait for it…egg whites. Or, better: albumen. Take an egg, separate the yolk from the white and use the yolk to make fresh pasta. Whisk the egg white until it’s firm (‘soft peaks’), and let it sit for a couple of hours that way in a bowl. Then pour the liquid that has collected at the bottom of the bowl into a suitable jar; discard the foam. You now have the albumen that is perfectly suited for subbing temporary support sheets.
The albumen needs to be hardened when it’s applied to the sheets, as otherwise it will dissolve away in the warm water development bath. There are many ways of hardening the albumen, but a quick and easy method uses the same DAS sensitizer also used in the carbon tissue itself. Adding a little of this to the subbing solution (which is a little albumen in a lot of water and maybe a drop of photoflo) will harden the albumen as the sheets are hung to dry in daylight. It’s also OK to dry the sheets first (e.g. at night) and then expose them to UV to harden the albumen.
Space and equipment
For making the albumen, any kitchen bowl and a mixer will do fine. You’ll need a small jar for storing the albumen – I use empty food jars.
For the subbing procedure, you’ll need some trays of a manageable size. It’s not critical. I use plastic storage containers a lot because they’re easy to be had and cheap.
A clothes rack or a simple line and a pack of clothespins works well for hanging the subbed sheets to dry. This can be done in any room. Keep in mind that DAS-incorporated subbing needs to harden under UV light at some point for at least half an hour or so (longer is OK). The whole subbing procedure can be done in a room with daylight or artificial light, as you please. If working under daylight conditions, the DAS-sensitized subbing solution will have a useful lifetime of maybe just an hour or so.
Protect the floor from dripping gelatin with an old bedsheet, some newspapers etc. You don’t want hardened albumen all over your floors, I imagine – although it’ll clean up easily enough, especially if it’s still wet.
Final support preparation
This is my other favorite part. As with many alternative printing processes, you get to choose the paper you print on, which is very liberating (I find) when coming from silver gelatin printing. All (well, most) of those gorgeous watercolor and etching papers are usable!
Papers
What you’re looking for in a paper is a decent amount of strength or sturdiness. Other than that – just about anything would probably work. Heavier papers will be less prone to tearing and other damage than lighter ones, so start out with papers at least 200gsm. Feel free to sample the selection of etching, drawing, watercolor and printmaking papers your favorite shops retail. I’m personally very fond of Schut Laurier which is 250gsm and plenty strong enough for prints up to 8×10″ (and beyond).
Paper, of course, is a topic many good books have been written on as well, which illustrates how much complexity and technology is hiding behind that seemingly flat, white surface. But we don’t really have to go there, I think. Just pick up some papers you like. Give it a try. This is one area where carbon transfer is surprisingly forgiving – much more so than the metal-based processes like Kallitype etc.
One thing that won’t work for double transfer carbon (which I limit myself to in this blog) is transferrin to fixed out silver gelatin papers. These are often recommended for single transfer (dichromate) carbon transfer as a reliable and easy way to get started. However, the gelatin emulsions on silver gelatin papers won’t swell nearly enough to take the image from the temporary support. Well, they could, but you’d still have to apply an additional sizing layer (see below) and that removes any benefit this option would have over ‘fine art’ papers.
Sizing
As with the temporary support, these papers do need to be treated before they can receive the gelatin image from the temporary support. In this case, the pre-treatment consists of applying a fairly heavy layer of gelatin that is allowed to swell nicely just before the transfer is made.
The same gelatin as the one for tissue making can be used. Gelatins with little color are preferable – unless you prefer the yellow tint that the gelatin imparts to the paper. For the double transfer procedure, the gelatin does not have to be hardened as for single transfer (dichromate) gelatin. So it’s really a single-ingredient sizing formula. Just gelatin.
Some practitioners use different gelatins for different purposes. For instance, Kees Brandenburg uses the GMW/Gelita Type #1 bovine photo gelatin for carbon tissue and the Type #2 porcine gelatin for sizing final support papers. I don’t find it necessary to use two separate gelatins, and would just start with one kind and then see how you get on.
Space and equipment
The same kind of space and equipment can be used as for the temporary support preparation and tissue production. Nothing is light sensitive in this operation, so any kind of space will do.
I personally prefer to size papers one big (e.g. 40x60cm) sheet at a time, by putting it on my (level) worktop, pouring some water over it and letting it soak in, then squeegee off the water, leaving the damp sheet. On the damp sheet, the gelatin sizing mixture can be poured. I spread it with my fingers and the same kind of comb I use for spreading glop.
Drying the paper requires some decent spring-loaded clamps if you’re sizing big sheets; they’re usually sold as gluing clamps or market-stall clamps. Small sheets can be hung to dry with regular clothes pins on any clothes line or rack.
Print finishing
DAS as a sensitizer has a few drawbacks (I mentioned cost), and one of them is that it stains. Badly. DAS is yellow to begin with, but upon exposure to UV, it darkens a lot and this will significantly tint the print. Usually, printers choose to clear this stain (it can of course be kept if you like it), and this requires some more chemistry.
The DAS stain is rather persistent, so it requires a ‘big gun’ from the chemical arena to break it down. The weapon of choice here is potassium permanganate, which is fairly common chemical. It’s used for emergency water purification (remember Bear Grylls?), combating disease in fish ponds (notably Koi), blowing stuff up…er…yes, it also has some inadvertent uses, and as a result, its trade is restricted. In practice, this means that if you buy it in the EU in any significant quantity, you need to sign a declaration that you don’t use it to make explosives, drugs etc. It’s a minor inconvenience, and fortunately, the stuff is still quite cheap by all accounts.
The permanganate is made into a very weak (and beautifully purple) solution in which the print is soaked for a minute (or two) while it’s still on the temporary support. This makes the DAS stain sensitive for the following clearing bath.
The clearing bath consists of sodium metabisulfite, which is another common (even more so than permanganate) chemical, available from e.g. brewery/winemaker’s stores. A pinch is added to a jar of water and the print is soaked in this after the permanganate bath. In this second bath, the yellow stain disappears.
So just two chemicals – potassium permanganate, and sodium metabisulfite (or just sodium bisulfite – it’s basically the same thing in this context).
With hand-made prints, there’ll be some imperfections here and there. For retouching prints, use any kind of spotting dye or paint you fancy.
Space and equipment
A glass bottle for storing the permanganate solution is nice; it’s best to use a brown glass bottle since the permanganate solution will decompose under influence of UV light. Alternatively, just store it in a dark cupboard and only take it out for use.
Any kind of trays will do for clearing the images. Dry finished prints the same way as you’d dry anything ranging from tea towels to silver gelatin prints.
Shopping list
That’s it! Long story, still, isn’t it? Well, let’s condense it into a shopping list. It’ll be less intimidating that way. But at least you now know why you’ll be looking for the following items, and what to look for them in each of them.
Carbon tissue
Materials:
- Gelatin; 250-300 bloom. The whiter, the better.
- Colorants; i.e. India ink, watercolor paints, color pastes etc.
- DAS sensitizer powder. Start with 25g or 50g and buy more if the carbon virus catches on.
- Sugar; plain, white crystal sugar is fine.
- Yupo sheets.
- Ethanol for spraying glop when degassing. 96% fuel ethanol is fine.
- Glycerin (optional).
Tools/space:
- Glass jars for melting glop.
- Flat and level work surface for pouring tissues.
- Hot water supply (cooker, tap).
- A spray bottle to mist the bottom of your Yupo sheets, and another one to mist the surface of the glop with ethanol when degassing.
- A decent squeegee to squeegee the Yupo to the worktop.
- A hot plate or sous-vide stick.
- A comb for spreading glop.
- A scale for weighing materials. Precision at least 0.1g, but 0.01g is better.
- A space for pouring tissues that can be made free of any UV light.
- A dark drying space for the tissues.
- A fan for the drying space.
- A contact frame for exposing prints.
- A UV light source for exposing prints; a >100W 365nm LED floodlight is nice.
- Sunglasses.
Temporary support (film)
Materials:
- Transparent plastic film sheets. Pretty much any kind will probably work as long as not silicon-coated.
- An egg. You only need the albumen. Liquid egg whites sold in a carton will also work.
- More DAS. But you already got that covered.
Tools/space:
- Bowl and mixer for making albumen.
- Jar for storing albumen.
- Trays for subbing sheets.
- Drying rack and clothes pins/clamps for drying subbed sheets.
Final support (paper)
Materials:
- Any beautiful fine art paper(s) of your choice heavier than 200gsm; watercolor, etching, etc.
- More gelatin. Same as for carbon tissue is just fine.
Tools/space:
- The same glass jars (for melting gelatin), comb (spreading it), hot plate sous vide stick (melting gelatin), flat and level work surface and drying rack as for the tissues and temporary supports.
Print finishing
Materials:
- Potassium permanganate for print clearing.
- Sodium bisulfite for print clearing.
- Spotting dyes, watercolors etc. for retouching.
Tools/space:
- Trays, drying racks, etc. as used for previous steps.
You’ll mostly need patience, perseverance and potentially a shoulder to cry on from time to time when things frustratingly don’t work the way you imagined they would. That’s going to happen a lot with this process. It’s all the more rewarding for it, though.