Wheat paste—the practical side of it, for now. You can make all kinds of pastes from wheat and other starches; some are cooked, some are just mixed with water, some are pre-cooked so that you can just mix them with water. One sort doesn’t necessarily serve all purposes, and certainly not all binders. And within each sort there will be different properties according to where the starch came from, how much water was added, how long it was cooked, how long ago it was made, and so on. You can use it on its own, or mix it with PVA.
We’ve been making paste at 10% weight-to-volume, with the standard batch being 10 grams of paste & 100 mL water. You could probably find as many recipes as there are binders and conservators; just try one out and see if it works. I know people who make their paste very very strong but only use it after letting it sit for a day, others who make it strong and use it very dilute, and still others who make it less strong to begin with but use it full-strength. Some of that will depend on what you’re doing: you may want to use a more “dry” paste to avoid introducing a lot of water, or you may need a very thin film and so need the strength of the paste to be such that it holds even when very dilute. But some of it will just be personal preference and what you feel works best for you. All this is to request that you please take the following with a grain of salt, and it’s not any better or worse than someone else’s method. (If anyone else wants to weigh in, please do!)
Option (1): Weight out the paste in a beaker (tare the balance first) and measure the water in a graduated cylinder. The amounts don’t have to be exact.
Pour the water into the paste beaker, and stir well. At this point you’ll have small starch particles suspended in water, and tending to sink when the beaker is not stirred. Some people let this sit a bit before cooking. If you’re really precise you might cover with a lid to keep water from evaporating while it sits.
Set the heat on a hot plate or other heat source to high, and stir constantly. After a while you’ll hit the gel point, at which the grains of starch burst and the mixture thickens and becomes translucent . The longer you cook it, the thicker it will get. Larger batches need to be cooked longer. Be careful to stir all the way at the bottom or the paste down there will stick to the glass and burn.
When I’m satisfied with the paste, I keep stirring off the heat as it cools down. This makes straining easier.
While it’s hot, it’s quite soft, but if you let it cool to room temperature undisturbed it will be stiff enough to pick up in pieces between your fingers:
Option (2): Do everything like in the above but in a self-stirring sauce maker (Cook’n’Stir is the traditional one in the States but it’s harder to find than it used to be). Advantage: saves your arm the stirring, and frees you to do something else while it cooks. Disadvantage: less of a direct feel of how stiff the paste is. I gauge by color and by the noise it makes as it starts to stick slightly to the blade of the stirrer. When I used Zen Shofu it would tend to make strings as the blades pulled it around when it was about done, but the starch we’re using now doesn’t do that.
FINALLY: if you stir the paste until it’s room temperature and use it right away, you may not need to strain it. I prefer to stir just until it’s not so hot, plunge it in water, and then pull off pieces to strain as needed. I find that my paste lasts longer that way, about a week as opposed to a few days. If I know I won’t use it all right away I pack some into a syringe, which keeps the air out until I need it, and then it can last two weeks or more. You can buy a horsehair strainer like the one below (but they’re expensive) or make something yourself to approximate it. Essentially you need to be able to push the paste through a fine mesh to break it up into little bits. This gives you the most smooth paste.
The paste before straining:
The paste after straining (push it through the mesh several times, until there are no lumps):
Ready to use!
Where to buy wheat starch:
I’m used to using Zen Shofu from Talas (currently $20.85/lb, or $20.50/lb from Bookmakers)—it makes a particularly smooth and sticky paste. I’ve also used Aytex-P from Talas ($5.60/lb) and liked it. We get our wheat starch at West Dean from a chemical supplier (I’ll look it up if anyone’s interested) in the UK. Shepherds sells Zen (Jin) Shofu for £5.11/.5 lbs—-which is slightly cheaper than the US suppliers if you live here, but not after you factor in shipping if you don’t.