Glop, gloop, pigmented gelatin – whatever you name it: it’s that pretty awesome looking slithery stuff that forms the basis of a carbon transfer image. Looking at liquid, bubble-free glop at the right angle is a bit like staring into a black hole. It surprises me Anish Kapoor never caught onto it, really. Anyway, today is glop-making day again as I’m running out of 8×10 tissue. I took some pics and will (probably) follow up next time with tissue-making.
In a nutshell, carbon transfer works by selectively hardening a gelatin emulsion in which a pigment is trapped, so that the areas that are hardened more also retain a heavier layer of pigment and vice versa, and this creates our shadows and highlights. That’s simplifying a complicated process to an almost hilarious degree! What we can take out of this, is that we at least need gelatin and a pigment, and mix them.
Then, we also need some other stuff. To melt the gelatin and be able to manipulate it, we need to dissolve it, and water is the most convenient solvent here. Thinking of it, I’m not sure if anyone ever tried other kinds of solvent for this process. I sure haven’t heard about it.
If you take a fairly heavy layer of gelatin (let’s say 0.1mm dry height, which is fairly typical for carbon tissue), it turns out the be rather stiff especially in dry weather. So much so that it will actually crack if you bent it too much. Which is something you might notice if you try and bring the tissue into contact with a negative. Try that with a tissue made out of only gelatin and pigment! So we need a plasticizer of some sort, to keep the tissue supple even when dry. As far as I know, sugar has always been used for this, and continues to be used today. Alright, I didn’t specifically look for it, but back in 1905, A.M. Marton wrote a rather nice manual about carbon transfer and he does mention the use of sugar.
Not only sugar has been used; glycerin has always been a popular additive to glop as well, for more or less the same reasons as sugar – right? This is what Marton had to say about glycerin:
Glycerine makes the tissue very pliable and causes it to adhere better to the support, and also makes it easily soluble during development, but it must be added with case; while it gives contrast and greatly adds to the vigor of the prints, it will also cause a loss of half-tones, and considerably retards the action of light upon the tissue. Use from a half to one per cent.A.M. Marton, 1905: A new treatise on the modern methods of carbon printing., p37
Any words of wisdom on sugar from the same authority of yore? Well, sure! Hang on – from the same publication and further down the same page:
Sugar is sometimes used instead of glycerine; it makes the tissue pliable, easily soluble in hot water, and adds vigor to the prints. Use from one to four per cent.
You’ll have to excuse me for not being able to accurately explain what ‘vigor’ means in this context. Marton uses the term liberally, and as far as I can tell, it would equate to things like ‘crispness’ or ‘brilliance’ and similar qualifications. If I had to put it into technical terms, ‘contrast’ or perhaps also ‘microcontrast’ would probably come close.
Be all that as it may, it’s 2022 now, so let’s not remain stuck in the early 1900s. And today we have other authorities, which allows us to be a bit more specific and probably accurate about the sugar / glycerin thing. Cue Sandy King, carbon transfer deity of the present: “many people are confused as to the role of sugar and/or glycerin.” Alright, I confess guilty! Could you help me out, please?
Sugar is added so that water can enter the gelatin emulsion faster. This is a great help in warm water development as the gelatin emulsion will faster than if the tissue contained no sugar. Sugar is therefore working as a plasticizer, or dispersant. All tissue needs sugar, or some other plasticizer. Sugar works well and is common and inexpensive so there is no reason to look for an alternative. 20-30 grams of sugar per liter of glop is about what most people use, though as high as 50 grams per liter has been used..
The purpose of glycerin is to hold some moisture in the tissue, so it functions as a humectant. People who live in climates where the relative humidity is over about 35-40% don’t really need to use glycerin in making tissue. And even in very arid climates very little is needed. Glycerin will keep the tissue pliant but the down side is that it retards drying time. Basically I would only recommend adding glycerin to make carbon tissue when your work conditions are very arid, say 30% RH or less, and even then never add more than about 5 grams per liter of glop.Sandy King, 2009, via groups.io
So, sugar and glycerin have different purposes. The sugar mostly or even only serves to help in the actual transfer process, when the exposed tissue is soaked in the mating bath. Glycerin helps us with the stiffness of a gelatin emulsion. Also note that King suggests only adding glycerin to glop in very arid climates, but later also indicated using both side by side himself:
And if the RH in your workspace is now 70º you certainly do not need to use any glycerin at all, most likely about 20-40 grams per liter of sugar is all you need. The RH in my working conditions range from a low of about RH 25º in the winter to as high as about R˙ 65º in the summer so I use both sugar (40 grams per liter of glop) and glycerin (2.5 grams per liter of glop). On the whole this works better for me year around than using only sugar, and even in RH of 65º or more I only need to dry after sensitizing about two hours, compared to about 45 minutes when the RH is 25º.Sandy King, 2021, via groups.io
Until very recently, I never added any glycerin to my glop and only used sugar. This worked OK, but my tissue did have the tendency to become a bit wayward, depending on weather and the support they are poured onto. Lately I poured some tissue onto Yupo and as the weather turned particularly dry and I had left the tissues out, they actually overdried and became nearly impossible to work with. So I heeded King’s remarks and also started adding glycerin to my glop. And this, then is the recipe I’ve been using for my last batch, and the same I’ll be making today:
- Gelatin, technical grade: 8%
- Sugar, food grade crystals: 5%
- Glycerin, 86% solution from drugstore: 0.25%
- Pigment in the form of Talens India ink: 1%
I’ll be making two batches of 500ml because I find somewhat smaller mixing vessels / beakers nicer to work with than larger ones. And they store more compactly! A total of 1000ml of glop should give me approx. 16 tissues of a little over 8×10″ and maybe some smaller ones for 4×5″ poured from the leftovers.
I start with measuring the gelatin and sugar. I generally mix them dry and then add water to let the gelatin bloom. The sugar will dissolve at some point in the process, I’m sure.
Add water, and let bloom. I generally add about 300ml of water to the gelatin/sugar mix, so I have a 200ml volume to play with when adding the ink and rinsing its measurement cup (see below).
Now for the pigment; I mostly use Talens India ink. There are a few reasons for this. Firstly, as a liquid, it’s easy to measure, and in this way easier to work with than e.g. acrylic paint. Secondly, acrylic paint, which I also use sometimes, tends to leave an oily film on top of the tissue. It doesn’t show up in the prints, but there’s evidently things in the paint that aren’t necessary for the carbon transfer process and who knows they do actually interfere with it in a way I simply haven’t spotted yet. Thirdly, this ink has a very fine pigment dispersion and the carbon black pigment actually remains in dispersion very well even when diluted. This is one of the problems when using acrylics or home-made dispersions: they may be stable when undiluted, but as soon as you dilute them, they may drop out of ‘solution’ (not being a true solution). Fourthly, if it’s good enough for Calvin Grier, it’s good enough for me! See his remark in his pigments store about the black pigment: he literally recommends the very ink I had been using for a few years already. Convenient!
I measure the ink together with the glycerin into the same small beaker. The bottle of ink shown above is also the reason why I decanted some ink into a different bottle as shown below. The original bottle is very inconvenient when doing accurate measurements; a wide-mouthed small jar is much more convenient for this.
After blooming the gelatin and mixing in the pigment, it’s time to melt the gelatin. I use a simple water jacket fashioned out of a plastic storage box for this, which I fill with hot water. The temperature is not critical as far as I can tell, as long as it’s not scalding hot, I suppose. I generally eyeball a mix of boiling and cold tap water that probably ends up being between 50C and 65C. I use glass stirring rods to stir periodically. Lifting out the rods also helps to see if the gelatin has melted; if it hasn’t, there will be translucent little blobs adhering to the rod along with a smooth, thin film of glob. Continue melting until all blobs have disappeared.
Now, the wait begins. Because as the gelatin blooms and melts, lots of air is released. Lots, and lots, and lots…in the form of millions of tiny bubbles. Look at that foam:
In my previous carbon transfer stints, I used to use water jackets to assist the outgassing process. Because the gelatin needs to remain melted, and this means we need to keep it at above 37C for as long as the outgassing period. The duration of this period isn’t all that critical, as long as it’s long enough. I find an hour is the bare minimum, but I’d stick to at least 2-3 hours if possible to get rid of the bubbles. Replenishing the water jacket with hot water can get tedious. Some resort to using insulated boxes and whatnot for the purpose, but since I do some SMD soldering from time to time, I happened to have an actual hotplate around that proves to work perfectly for this as well:
We can get rid of the bubbles a little quicker by popping them. Since individually popping millions of tiny bubbles sounds (a) tedious and (b) requires insane motor skills, I resort to the brute force way and spray them to oblivion with a little sprayer filled with bio-ethanol.
And now, we wait. So, I’m going to have lunch, do another small bugfix on some embedded software, take a shower and then…hopefully come back at a later moment to pour some tissues.