This might get long…
I print carbon only a few weekends a year, so I thought it would be worthwhile to make a visual log of the process before I forget it all. I have a written journal for carbon stretching back to the beginning, filled with meticulous notes of every step and every change along the way. Not surprisingly, the journal is increasingly tedious to wade through when I decide to make a few prints. So this is an attempt to digest what is working well for me at the moment into a relatively brief overview.
I get emails about this printing process too, so if you want to follow along here’s a list of some stuff I’ve found very useful, none of which is expensive. But be aware that this isn’t intended to be a practical guide, there are many much better sources than this to learn about particulars of the carbon process. And a quick note on units: I try to use metric whenever possible, except for imperial format sizes common to print sizes or film formats, or if a source for materials uses imperial units in their product description.
- Granite slab for the pour table (sink knockouts can be had for free from countertop fabricators). These are nice because they are dead flat, don’t sag under their own weight like large piece of plate glass. The slabs also have thermal mass, so it can be kept to a surprisingly constant temperature outside the ambient for extended periods. This helps in hot climates, gives the tissue a fighting change to gel. It also helps to preheat the slab slightly in really cold weather, to give a chance to spread to pigmented gelatin (glop) out before it starts to set. The downside- they are heavy. Moving them around can be a chore.
- Magnetic stirrer and various stir bars. I dilute the pigment the night before, to give it a chance to disperse thoroughly. The stirrer really makes short work of blending pigments, dry or in suspension. A heated unit might be useful, but they are typically more expensive.
- Crockpot- helps maintain temperature baths around 45°C. Anything with a “Warm” setting has potential- most kitchen ranges can’t keep such a low temperature consistently. On the warm setting, my Crockpot will keep a volume of water at 45°C for hours with out the need to fiddle with it or keep a close eye on it.
- Thermometers. Instant read, waterproof are nice.
- Graduates and mixing vessels- having a nice range of each really helps. I usually mix a so called ‘parent’ batch in a 1-gallon pail, then divide this into individual pint-sized containers for the final resting period before pouring the tissues.
- Filters- I have had good luck with those permanent coffee basket filters, but much will depend on the sort of pigments that are used.
- Mayer rod. Around $30 each for a decent size, 1/2″ diameter x 28″ length. These are readily available from RD Specialties, even custom sizes. I use the gapped version- they are less expensive than the formed rods, are plenty durable for non-industrial use, and are available in a greater range of wire diameters than the other styles, which will allow to draw to a thicker wet film height required with carbon printing. Can’t say enough good things about RD Specialties- I received 3 custom wound rods in under a week. I use a #200 for the tissue, and a #100 for sizing paper.
- Alternately, tissues had be poured mold-style, with some sort of frame used to screed and form the gelatin at the desired thickness. I’ve used magnetic strips (with a metal pour table). I’ve also had good consistent results using a pouring frame cut out of a vinyl desk blotter. The vinyl grips the tissue substrate pretty well and contains the glop without much bleed-back. The mold method is best for really thick tissues that give lots of relief.
- Squeegees. The tool of choice for mating the tissue and final support paper, but also useful for other steps during the process.
- Scale and assorted measuring gear- Sometimes the trickiest part of the whole process is measuring the pigment consistently. I prefer to measure by weight instead of volume. But getting the pigment out of the container to be weighed isn’t always easy. Cheap pipettes work well on thin pigments like india ink. For thicker pigments like the Kremer pigment pastes, diluting with gum arabic may make it easier to pour out for weighing. Tube watercolors are the easiest by far- just squeeze the tube into a tared-out vessel on a scale. But they are also among the most expensive types of pigment.
- Mixing tools- silicone spatulas, stainless steel whisk, things that resist pigment staining. Even though you could snack on the glop right up to the point you add the pigment, it’s probably a good idea to dedicate containers and utensils to just this purpose. A wood spoon does help for skimming the gelatin as the foam will really cling to the wood, but it’ll get irrevocably stained.
- UV light source- For exposing the tissues. Can be as simple, portable, and inconsistent as the sun. Or as complicated, heavy and stable as a plate burner. I made a simple UV printer that uses an array of UV fluorescent bulbs. Post on that here- https://colinflanarygraham.com/darkshop/?p=337
Raw materials-
- Pigments. While learning what suits your palette, good pigments are usually available locally, or the big web art suppliers like Dick Blick or Jerry’s. I like using a blend of M Graham tube water colors available at the local art supply and Kremer pigment pastes bought directly from the manufacturer. Choosing the right pigment is important, as is the binder. Carbon printing gets it’s name from the carbon pigment- Lamp Black, Furnace black, or PBk7 pigment is the byproduct of incomplete combustion. Soot, essentially. It’s a much more dense black pigment than Bone or Mars black. It’s also a nice neutral black. To give the black a cold or warm tone, a secondary pigment is often required. I like Kremer’s brown iron oxide paste for a warm tone. For a cold tone I use a good phthalocyanine blue shade like M Graham PB15:3. I’ve also been know to give carbon prints a green cast- reminiscent of a un-toned Brovira silver gelatin print developed in Ethol LPD. Anyway, a cool thing about carbon is there are no color restrictions. Handprint.com is a great source for finding reliable pigments, their granularity and lightfastness ratings. Some pigments are really much too granular- a wash coat of Dick Blick India ink looks like it leaves a trail of coffee grounds behind the brush, which is too bad because it’s a nice easy warm black, straight from the bottle. But I may have just gotten a bad batch. The Kremer and M Graham WC pigments are very uniform and smooth by comparison. I test every pigment before committing it to a batch of tissue. Making a sample book of wash coats is a good way to make a record of pigments and concentrations, how well they disperse and how water soluble they are. There are a few India inks use shellac as a binder, which isn’t compatible with the process. It also worth noting that print gloss can vary by pigment used, watercolors and india inks seem to produce glossier prints, while the Kremer pigment pastes are less glossy.
- Gelatin- Bulkfoods.com sells a nice 250 bloom gelatin that is clean and consistent. 5lbs makes a lot of tissues, and sizes a lot of watercolor paper.
- Ammonium dichromate: This is what make the tissue light-sensitive when printing. Don’t be alarmed, but you might have to fill out a DEA form to order it. I honestly can’t remember because I originally ordered a pound of the stuff from Photoformulary, and it’s lasted almost 10 years. Only need to fill the form out once, they keep it on file afterward. A little goes a long way: I make a 20% solution with distilled water and store it in an eye-dropper amber bottle, literally dispensing it drop by drop.
- Formalin- “100% Formalin” is really diluted formaldehyde, about a 40% solution. Formaldehyde is a tissue fixative, so this is nasty stuff. I only use it for hardening the gelatin sizing for watercolor paper, which makes it resistant to the hot-water developing step of the process. If you use fixed-out photo paper for the final print support you can skip this step. I was actually able to find some formalin locally at a pet supply store, where it’s packaged in even more dilute solutions as an anti-parasitic. Some printers size with plain gelatin, the dip the cured paper into a formalin bath. I like adding the formalin right to the sizing and doing it all in one step. This is where a detached garage comes in handy- unless you have a lab-grade fume hood, you really don’t want to use this stuff in the house, or to even let the paper dry or cure in the house. The fumes are unhealthy. There are some less noxious alternatives, but I like the formalin- and like the dichromate a little goes a long way- so I haven’t experimented too much. But if you are careful it’s no more dangerous than most photographic chemistry. And formaldehyde is also used in the stabilizer in the C-41 process, and part of the pre-bleach “conditioner” step in the E-6 process as a dye preservative.
- Miscellany- 70% alcohol, sugar, distilled water. The alcohol is both for diluting the concentrated dichromate, and also helps in dispelling air bubbles before pouring the tissues. I think it is also a tissue preservative. A few batches I’ve made without alcohol have molded fairly quickly, while I have 3- year old tissue made with alcohol that are mold-free. The sugar is a plasticizer, keeps the tissues from drying out and becoming brittle.
Printing materials-
- Tissue substrate- This is the base the pigmented gelatin is poured on, which acts as the tissue’s backing through exposure and up until the point the tissue is literally transferred to the final print support. Yupo, a synthetic watercolor paper, is ideal for this. I ordered 100 sheets of the 25″x38″ 68lb text version directly from the manufacturer. It’s an unusual size, but once cut in half it works well with my setup. Also drafting delrin works well. I like pouring big ‘parent’ sheets and cutting down to whatever size I feel like printing that day. I use digital negatives, so some days I’ll print 16″x20″, other days 5″x12″. This complicates drying and storing, but the extra work is worth it for me. Other printers make tissues specifically sized for in-camera large format negatives, since they will reuse the substrate they can use more expensive but more durable materials like fixed-out film. In short, anything dimensionally stable, water proof, and easy to work with will probably work well. Extra points for materials that don’t crease easily, and resist the curling that happens when the tissues dry, and are clean or are easy to clean.
- Paper- For final transfer. I use only a single transfer, so either watercolor paper, Yupo, or fixed-out photographic paper will work. The final support should be able to move with the gelatin, be sized with a suitable material that can bond with the exposed tissue, and archival. I don’t like using fixed photo paper, because no matter how much you wash it, the paper’s lifespan has been compromised by the fixer. Apparently fixer does things to paper that simply can’t be washed away. I use gelatin-size watercolor paper for the final support. But it’s not a compromise, I’d use WC paper anyway. I just like the texture, sheen and surface better than photo paper.
- Mylar- the printing times can be long, warm and this can cause the tissue to stick to the negative. A thin sheet of mylar between the tissue and the negative ensures that if the tissue is going to ruin anything, it’s only a piece of mylar. Some people use Krystal print bags. I get the thinnest mylar available on a roll from Talas, .002″. It’s available on a relatively small 20″ x 50′ roll.
Here’s a basic recipe, enough for seven or eight 48×60 cm tissues. In total it’s less than 1% pigment, but the Kremer pigments are highly concentrated. I blend the Kremer lamp black with the water color lamp black to reduce print gloss. A common pigment load for watercolors and India ink is about 1-1.5% pigment concentration. Note, this formula is good for negatives with relatively low a Dynamic Range of 1.6-1.8 or so, and with a printing environment of between 60-90% RH. I use digital negatives, and the DR is the practical limit of how much UV-blocking ink my Epson 3800 printer can throw down without artifacts.
4g Kremer lamp black
2g Kremer brown oxide
9g M Graham lamp black
1600 ml water
160g gelatin
56g sugar
10ml isopropyl alcohol, per 200ml pour
Sugar and pigment are the main variables. Most glop recipes I’ve seen use a 10% gelatin solution as the base. Generally speaking, the pigment load has an impact on contrast, and the sugar load is relative to climate, so a drier environment could need more sugar, or even additional plasticizers such an glycerin. From my experience, too much sugar can lead to excessive moisture retention, which makes drying difficult, and leads to print burnishing and mottling. Too little and the tissues curl into a tight roll, and can be infuriating to work with- they can actually crack while trying to register a negative on them for printing. Too much pigment can dull the sheen of the print. This can be helpful if you want a matte look, or are trying to balance the sheen between the sizing of the paper in the highlights and the tissue in the shadows. Too little pigment and you can expose all the way through the tissue to the base and still never get a convincing black. But pigment loading isn’t the only contrast control in carbon- the dilution of the sensitizers is very helpful in tweaking the contrast. With digital negatives you can tweak contrasts curves. More on these later.
Since carbon printing is for all practical purposes a 3 dimensional printing process, actual tissue volume is also consideration. Many printers like to pour really thick tissues to maximize this effect. The pigment load in thick tissues can be a little tricky- too much and you only expose a few mil deep and just waste most of the tissue and pigment, too little and you never get a convincing black and will risk exposing through all the way to the base, in which case the tissue will never separate in the transfer. Anyway, to my eye print relief is now a little tired. Admittedly I was first attracted to carbon for the spectacle of the relief, but I stayed interested in it for the excellent tonal scale. And even without the relief, carbon is capable of astonishing subtlety in the print surface.
Mixing steps-
•Set aside 8-10 hours. It take a long time to make this stuff, but 90% of it is just waiting for things to happen. The bulk of the time can be planned to happen overnight, or I suppose you could run the Crockpot while off at work- that’s what they were invented for after all- but I’ve never been comfortable doing either so I tend to make tissues when I’m working around the house all day, etc.
•Mix pigment in 600ml of room-temp water in covered quart yogurt container, stir with magnetic stirrer for 1 hour or so. I like to do this the night before and let it rest and disperse overnight, but it’s not critical. I also like to pour the remaining 1 liter of water into an uncovered graduate and let it de-gas overnight. While this can’t hurt, it probably doesn’t help all that much. The biggest time-sink is waiting for the millions of bubbles to dissipate from the glop, so it makes me feel better to pretend I’m being proactive.
• Next morning, bloom gelatin in the liter of degassed water for ½ hour. This is to swell and soften the gelatin before melting. This is a holdout from my kitchen days, where you had to ‘bloom’ the gelatin before adding it to a recipe. I keep meaning to try adding gelatin straight to hot water to see if it speeds the process any. But most literature on the carbon process also recommends blooming the gelatin.
• Mag-stir pigment solution again while gelatin is blooming and melting. 2 hours or so.
• Boil water in kettle. Place gelatin container into Crockpot and add boiling water around gelatin container (not in it). You’re just making a water jacket to help melt the gelatin. Start chopping gelatin with spatula and stir constantly until uniformly melted. Add cool tap water as needed to make water jacket temp 50°C. Temper gelatin mix in Crockpot on low setting for 1/2 hour, stirring frequently, until fully dissolved. This can take some time at low heat. Be careful not to overheat, cook or otherwise stress the gelatin. Apparently that will do odd, irrevocable things to gelatin, although I’ve not tested it.
• Blend in pigment solution to gelatin. I like using a whisk to incorporate. It will get frothy- this also help accelerate the de-gassing process. Leave uncovered to dissipate bubble. Temp in 45C range (low setting when uncovered).
• Add sugar and whisk again. Turn Crock to warm and leave uncovered @ 40C until froth dissipates (at least 4 hours- this a good step to do overnight if you are so inclined). It’s going to get filtered later, so I don’t worry too much about bits of stuff getting into it, but then I don’t have any cats.
• Or you can just skim the foam. It’s easy to skim with a dedicated wood spoon. This foam is some seriously sticky stuff, like cotton-candy sticky, so it almost jumps on the spoon. This will shave a few hours off the procedure. The foam doesn’t cling as well to plastic or metal utensils.
• Blend solution completely with spatula, scraping down sides and bottom to incorporate all pigment and mix thoroughly. Preheat basket filter and another clean 1 gallon tub, then filter glop into new tub.
• Pour off into smaller portions, 200ml. Those short, wide sour cream pints work well. They aren’t top heavy and can bob around in the Crockpot without tipping over. At this point I’ll loosely set tops on the containers to keep crud out of the solution.
Pouring steps-
• Make sure glop is in 40° to 42°C range and free of bubbles. Roughly 15 minutes before pouring a tissue, add 10ml of 70% isopropyl alcohol to glop per 200ml portion and stir well, place back in water jacket. Leave stir-stick in container for ID, if the containers are bobbing around in the water jacket, it can be easy to loose track of which is which. I don’t like adding alcohol to all the containers at once. What can I say. Baseless superstitions are highly addictive.
• Preheat oven to warm or lowest setting. Place foil on diagonal on rack to set Mayer rod in (mine barely fits in the oven, even diagonally). The foil is to protect the rod from contaminants while preheating. Alternately, you can warm in a bain-marie, if you have one long enough for the rod. I thought about making one out of a length of ABS pipe with screw caps. But then it will get wet, and drying it poses the risk of transferring lint or hair to the rod, and excessive cooling in the time it takes to dry it and make sure it’s fuzz-free. I’ll keep using the oven.
• Meanwhile, level and clean pour slab. I like those composite shims, waterproof and indestructible. Leave 3″ of room on either side for rod handle. I like to set the slab on three nested (for strength) 12″x16″ trays, then stick the shim between the marble and top edges of tray- that way I can slide the whole thing up and down the sink if needed without having to re-level it. This also raises the working height, making it easier to push the rod without banging my head on the cabinet above the sink. Also makes moving the slab in and out of the sink much much easier.
• Rinse Yupo with cool 70F water. Squeegee Yupo and wipe to an even damp sheen with damp microfiber cloth. This will help the glop flow quickly and evenly. Check surface at a glare angle to make sure there are no drips, puddles or hairs on the support.
• I do these following steps as quickly as possible to maintain preheated temps: Lean rod upright against cabinet. Do not set down horizontally; sitting on the table top it may cool too quickly, and if it’s set on a towel for insulation it will probably pick up dust and lint, so it’s best if it’s only supported by the ends of the handles. It’s very important to give glop a final thorough but gentle stir to make sure pigments are distributed evenly. Set in tray lined with towel to dry outside of container. Set Mayer rod at base of Yupo on appropriate side. Make sure container is dry and wont drip water onto Yupo, then pour with container close to support, gently but quickly and as evenly as possible. Pour to edges of Yupo, using fingers if needed to dam edges. This will help to get coverage with one pass. Then steadily push rod to top. If needed, return back to starting position to coat entire sheet. Don’t roll, just push. Set rod aside for cleaning, but don’t pass directly over surface of tissue to avoid drips. I’ve thought of trying one of those pancake batter dispensers that pour from a opening in the bottom of the container, but that’s probably more trouble that it’s worth.
• Let set up for 10-15 minutes. Cover with a dust screen if needed.
• When set, trim away extra. This varies, but basically you need to scrape away enough from two opposite margins to provide room for clothespins. (The 28″ ‘Smoothee’ window film squeegees work well for this.) Move tissue directly to foam board and set in drying rack to gel completely before hanging to dry. I made a foam board spacer, to keep the foam board from sagging and sticking to the tissues- the tissues are fairly heavy when wet.
• Add alcohol to next batch before prepping Yupo and preheating rod for next pour.
• After all tissues are done and have setup for an hour or so, hang to dry. Plastic clothes-hangers with spring clips work well, with a strip of Plexiglas clothes-pinned to the bottom of the sheet, to stabilize it against curling, and to provide a little extra weight if drying under a fan. The skirt/slacks press hangers look like they would work well. Due to the humidity here I always use a fan to dry the tissues, otherwise the tissues take a week to dry. With a fan, 48 hours or so is enough, even with the recent stretch of 90% RH. But in a drier climate with a lot of dust, a fan might be disaster.