How to make traditional gesso--with the traditional ingredients--for raised gilding in manuscript illumination.
So what is traditional manuscript gesso? It's a base used to raise up gilded areas in illuminated manuscripts and act as a size (glue) for the gold leaf to adhere to. It is the key ingredient in creating illuminations with a three dimensional effect and a mirror-like polish. It was not used in the earlier centuries of manuscript art, but reaches its full flourishing during the Renaissance period. And it is owing to the Italian artist Cernino Cennini that we have a recipe for manuscript gesso from the early 15th century.
The first step in making traditional manuscript gesso is slaking the plaster of paris. If you want to know more about this part of the process, consult Part 1 of this guide.
The slaked plaster is the primary ingredient of traditional manuscript gesso but there are several other ingredients, some more difficult to acquire than others. One of them you likely have in your kitchen right now: sugar. Just plain old table sugar like you put in your coffee. The sugar is what will make the gesso sticky when it is reactiviated during the gilding process. Some people use honey instead, but I learned to do this with sugar, so I'm sticking with that for now. However, the sugar needs to be ground into a fine powder first. You don't want big grains of anything in your gesso to mar the mirror polish. Also, in powdered form, the sugar will dissolve much faster. I use small amounts of sugar and grind it by hand in a mortar and pestle. It doesn't take more than 10-15 minutes to do.
I only keep a small amount of powdered sugar around (I use it in another form of traditional gilding as well) because it will clump readily, especially if you live somewhere humid. The powdered sugar you buy in the supermarket includes an anti-caking element for this exact reason, which is why you can't use supermarket powdered sugar in manuscript gesso.
You'll also need armenian bole, which is a red earth mineral that will add a touch off color to your gesso and is chemically neutral. I get mine from John Neal Books. You need only a pinch or two so even the small amount you buy will last you for years.
As a binder, you will need fish glue, also called seccotine. Some people use hide glue or parchment glue. Hide glue is available from various bookbinding and specialty art suppliers. Parchment glue is made of bits of old parchment that has been put through a disgustingly smelly process. There's only one supplier that I know of and it's very expensive. The trouble with both hide glue (or rabbit skin glue) and parchment glue is that they need to be reconstituted, heated, and kept warm. Fish glue, however, has the advantage of staying liquid at lower temperatures. I get mine from Kremer Pigments, a German company that has one store in the US (fortunately for me, it's in NYC). Like with the armenian bole, you don't need much, so buy the smallest bottle.
You'll need some distilled water, which is easy enough to get. The last ingredient, however, may be the most important and the most controversial. It's lead white or flake white. This is the powdered lead that was used in white paint for centuries and is now banned because it's poisonous when ingested or inhaled. Many people will not use it for that reason and substitute it with titanium dioxide. The trouble is, the lead white isn't used here for its opaque, whitening properties, like in paints. It's used because it's a soft material and retains its maleability. My understanding of gesso made with titanium dioxide is that it is more brittle and won't polish up to the same extent as gesso made with lead.
There are two sources of lead white that I know of in the United States. The first is, again, Kremer, where it is called cremnitz white. The other is Natural Pigments. This is where I got mine.
Because lead white is poisonous, I take some precautions. First, I wear a mask and latex gloves. Second, I lay everything out on a large piece of paper, which I can then bunch up with all the discarded materials and throw out in one bundle. Third, I wash nothing in the sink. Instead, I use wet wipes. You could use moistened paper towels too, but I happen to have some wet wipes that I need to use up. And fourth, nothing I use here gets used again for making anything else. Which reminds me: I need to buy new measuring spoons to put back in the kitchen.
Some other tools you'll need: a pipette, a palette knife or two, some acetate film (plastic paper, essentially), a grinding plate and muller, or a mortar and pestle.
The recipe is quite simple:
8 parts slaked plaster
3 parts lead white
1 part sugar
1 part fish glue
a pinch of armenian bole
as much distilled water as necessary
I lay out the plaster, lead white, and sugar in neat piles first to make sure I have the right numbers.
Then I mix them together and grind them on the plate to eliminate as many gritty bits as possible. Doing this now will make the final grind easier and faster.
At this point, I add the armenian bole. How much you add is about personal preference. The more you add, the easier it will be for you to see the gesso on your paper or vellum. However, the color of the underlying gesso will also slightly change the color of the gold you put on top of it. If you like your gold to have a redder tone, by all means, add more bole. I usually add a small amount, mix it, and then decide if I want to add a little more.
Once all the dry ingredients are well mixed together, I add the fish glue.
Once I have poured the 1 part of seccotine onto the pile, I use some distilled water to somewhat wash out the measuring spoon and make sure I get the full measure of the fish glue into my gesso. I use the palette knife to begin to mix in the wet ingredients, adding more distilled water with a pipette in small increments. You want your gesso wet enough to grind easily with the muller, but not too wet that it will slosh around or drip off the plate. Keep in mind, however, that as you grind you will likely have to add a little bit more water since the gesso dries quite quickly.
It's at this point that I usually think, why didn't I choose to make more? With the water fully mixed in, the quantity of gesso looks like a lot less. Unfortunately, my grinding plate is fairly small and so I run the risk of accidentally pushing ingredients off my work area if I use a measurement larger than a teaspoon. If you have a larger plate, then by all means, use a larger measurement. The important thing is just to keep the proportions the same.
I will mull all my ingredients together until I feel they are fully blended, I can feel no grit, all while trying to eliminate as many of the tiny air bubbles as I can. This is important for later as air bubbles in your gesso can be a real pain-in-the-ass to deal with when you're trying to gild.
The last step is to dribble little puddles of gesso out onto a piece of acetate. The acetate makes it easy to pull the puddles off once they have fully dried.
Some of my puddles are on the larger side, for when I need more gesso for a project. Just use your own judgement for how big to make them depending on how much you think you will use in one sitting.
To dry my gesso, I cover the acetate with a cardboard box and then stack heavy books on top to keep the cats from knocking over the cardboard box. Obviously, it will dry faster without the box, but you will also end up with dust all over your gesso. Once fully dried--and you'll know because it will peel off the acetate easily--you can put your gesso puddles into little wax paper or parchment paper packets, label them with the date they were made, and store them away in an air-tight container. They will keep forever.
Stay tuned for Part 3, to see how the gesso can be reconstituted and then used for gilding.
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