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Gesso recipe Hide glue recipe Slaked plaster recipe

Making a period style gesso
for use in raised gilding

By Maitresse Yvianne de Castel d'Avignon, OL

Paper is made up of many small fibers pressed together. Vellum also has an uneven texture to it. The only way to achieve a mirror polish with gold leaf is to apply something on top of your paper or vellum to smooth out the surface so that the gold leaf will not mimic the imperfections. Gesso is a time proven way to do this.

Combining a size, or glue, with an ingredient that increases the bulk, makes gesso. The first gesso was little more than red clay (Armenian bole) and glair mixed together. Different recipes evolved over time incorporating many of the same materials often used in paint making. Modern and more purified versions of many of the ingredients can be found at your local woodworking or hardware store. Learning how to make and use gesso is an art in itself. How gesso is made and what the various ingredients do will help you understand the material you are working with and how to make it work under most conditions.

Gesso is affected by weather conditions. Gesso made on a hot humid day will most likely not work well in the cold, dry climate of winter ... unless you adjust the gesso to suit the conditions. Something this simple can affect whether your work will turn out to be a masterpiece or a total disappointment. The amount of moisture in the gesso at the very moment the gold is laid on top is a major factor in determining whether your gold will stick or not. Honey or sugar are commonly added to period gesso recipes to impart a bit of stickiness and adds flexibility resulting in a less brittle gesso. The opposite of dry gesso is sticky gesso. If you add too much honey or sugar gesso will turn into a slow drying goo. Keeping a log book of the recipe you used and the weather conditions when you make gesso is a great way to keep track of the adjustments you make to get the gesso to work under various conditions and allow you to repeat good results and avoid disappointing ones.

If gesso is so hard to work with, why do people use it?

Because nothing gives the same results that you will get when raised gilding works. Just the chance that a spot of gilding will turn out to be mirror perfect is well worth all of the headaches you go through to try and achieve it. Even bad gilding looks good to most people. Sometimes the results of gilding are out of your control. Expect and accept the imperfections that WILL happen. Remember, the medieval scribe had to deal with finicky gesso too. Even in museum quality pieces you will see the same mistakes over and over.

What gesso can't do.

Gesso isn't a magic bullet that makes every attempt at raised gilding a success. Only with experience can you learn how to tell what causes a certain type of mistake and if it is correctable ... or how to gloss over the mistake to make it less noticeable. There are no short cuts and no promises, except the promise that when it works, nothing can compare with the beauty of raised gilding.

The Recipe

There is no single *right* recipe for period gesso. Weather conditions such as heat and humidity can affect how much of a certain ingredient is needed. Proportions are decided on by the scribe and are dependant upon the characteristics of the gesso that they like to work with. While the anonymous author of De Arte Illuminandi specifies fish glue in his recipe, Cennini cautions against using it in gesso. Modern research has shown gesso made with hide glue to be stronger than gesso made with any other glue.

The recipe I use is a period style recipe passed down through a lineage of SCA scribes. It is nontoxic.

Basic recipe for gesso
1 Tablespoon - slaked plaster (neutralized Plaster of Paris, chalk, or calcium carbonate)
1 teaspoon - hide glue liquid (woodworking glue)
coloring agent - bole, red or yellow ochre watercolor or gouache
6-12 drops of warm honey
1 teaspoon - distilled water

This recipe can easily be multiplied to make larger batches.

Measure out the slaked plaster and place it in a bowl. Mix the all of the remaining ingredients together in another bowl. Add the wet ingredients into the slaked plaster and mix thoroughly. You should have something similar to a pancake batter. You can add more water if you need to. The only adverse affect of adding too much water is the gesso will take longer to evaporate to a usable consistency. Use a mortar and pestle or muller if necessary and get all of the lumps out.

Test the gesso you've made and adjust it if necessary.
Honey - will make gesso more sticky and flexible
Slaked plaster - will remove some stickiness and fill in divots
Hide glue - will make gesso harder, fill in graininess and make gesso slightly stickier

Gesso can be used immediately or it can be poured onto plastic wrap in little spots or "buttons" and allowed to dry for later use. Gesso buttons should be stored in an airtight container. To reconstitute: place the amount of gesso desired in the bottom of a shallow glass or very small glass bowl. Place a few drops of distilled water on top. Let it sit for a while then place a piece of plastic wrap over your finger and break the gesso apart. Repeat this process until the gesso is completely broken down and is smooth enough for you to use.

When applying gesso, constant attention is needed to keep it at the proper consistency (similar to white glue). The water evaporates and will need to be replaced every once in a while. The ingredients in gesso will separate if not stirred during use.

It takes a bit of practice to make and use gesso. Don't get discouraged if you make a batch of gesso that works on the day you made it, but won't work when you want to use it. Adjust gesso buttons one at a time to suit the weather conditions on the day you are planning to use them. Sometimes, despite doing everything right, gilding just doesn't come out as nice as you expected it to. It happens to all of us and it happened to medieval scribes as well. Be prepared for "bad gesso days". They will happen. If all you are doing is getting more and more frustrated with a project, it's time to put it away for a couple of hours and go have some fun. Often you will return in a better state of mind and to better results.

Some Common Problems and Possible Solutions

** Gold will not stick **

*If the gold lays down nice, but falls off when you touch it, (sometimes in large flakes - often with a feathered edge) the cause could be a lack of moisture. Try applying the gold again; paying careful attention to how much moisture is in that area. You may even have to apply water with a paintbrush.(A common problem in low humidity - winter)

*If the gold will not stick to the gesso, but the glassine does. Your gesso may be too wet (either with too much water or honey) Wait a while for the gesso to dry out a bit and try again. If the problem was too much water, try not to get the gesso as wet. If the problem is too much honey (the gesso will be pliable when completely dry instead of hard and chalk like, sometimes a little bit of slaked plaster mixed into the gesso will remedy this situation.

*If the gold will not stick - no matter what you try. Larger areas can sometimes be painted over with glair and patched with another layer of gold leaf. Small areas can be painted over with shell gold. (Possible causes - You may not have stirred your gesso well enough and have a spot that is unable to hold gold or you may have gotten oil from your hands on the gesso.

** Uneven surface texture **

*Bubbles in the gesso can cause pits and divots. Do not use gesso if it has a lot of bubbles. Period practice was to mix a little ear wax into the gesso to get rid of a bubble problem. Your only other options are to wait for the bubbles to settle (if they ever do), or pop them one by one.

*Scratches, gouges and missed bubbles in the gesso. If they cannot be sanded or burnished out, they should be filled in with more gesso, allowed to dry and carefully sanded again before laying gold. If they are missed, you can try to fill the area with more layers of gold.

*Mottled appearance can happen if there is too much honey in the gesso or the gesso was too wet, but some gold stuck anyway. Try laying another layer of leaf over the mottled spot.

*Any number of smudges and spots can occur from burnishing your gold while the gesso underneath is too wet. If you are burnishing and the gold is just rubbing off or cracks start to develop in the gold...stop!!! Put the piece away overnight and try again tomorrow. If the problems persist, there is another more serious problem.

** Cracks in the gold **

*Sometimes there are imperfections in the gold itself. Several layers may be needed.

*The gesso may be too soft and the gold cannot stretch enough. If the gesso has had sufficient time to dry - at least overnight, reapply the gold and don't burnish with as much pressure.

*The gesso may be too dry and brittle. In this case the gesso is what is splitting apart, not the gold. You will usually hear crunching noises and feel the gesso breaking underneath the burnisher. Use a lighter pressure on the burnisher. Try to reapply gold over any existing cracks or patch with shell gold.

Don't forget, even imperfect gilding is gilding nonetheless. One way you can sometimes hide the mistakes and add extra dimension to the surface is through tooling or stamping an impression into the gilded gesso.

Hide glue

The hide glue liquid available at hardware and woodworking stores does not react the same in gesso as pure hide glue, which is often available as dry crystals or can be made at home.

Liquid hide glue makes a gesso that is far easier to work with. It reconstitutes easily and will remain in a liquid state for days, so long as you add water every once in a while.

Gesso made with pure hide glue must be kept warm during the application process or it congeals into a substance similar to jelly. Gesso made with pure hide glue is more flexible without being overly sticky in the short term. It may still crack after it is completely dry, a week or more, but is unlikely to crack during burnishing if is done within a few days of gilding.

Only through personal experience will you be able to decide if you have a preference for gesso made from one or the other types of hide glue.

If you want to make your own hide glue to use in gesso, or for other projects, it is easy enough to do.

4 ounces of vellum scraps
2 pints of distilled water
a small enamel pot
piece of loosely woven cloth (to use as strainer)
bowl - can be disposable plastic

Bring the water to a boil then reduce the heat to simmer and add the vellum scraps. Do not let the water boil once the vellum is added to it. This will reduce the effectiveness of the resulting glue. Allow this to simmer for one and a half hours (about half of the water will evaporate). Remove the pan from the heat and allow it to cool slightly. Strain it through a plain white piece of loosely woven cloth into a clean bowl. Let the glue to sit at room temperature in a cool, dry place out of direct sunlight overnight. It will congeal into a jelly. Turn the bowl upside down and remove the jelly onto a piece of plastic wrap. Slice the jelly into 1/4 inch slices and allow to dry out of sunlight. This will take several days.

To use the glue: take a slice or two of the dried glue and warm it in a bit of water. You can do this in a small metal or ceramic dish over a candle or on a stove burner. Once again do not allow it to come to a boil or it will be useless as glue.

An alternative storage method is to strain the glue into a jar with a tight fitting lid. Allow it to cool, cap it and store it in the refrigerator. If mold appears, it can be removed with a spoon and the remaining glue used. To reconstitute it all you need to do is spoon the desired amount into a small metal or ceramic container and warm it. It is not necessary to add water.

If you are using a pure hide glue based gesso you will have to repeatedly warm it. You may want to place a low temp glue pot or candle powered potpourri burner near your work area to help keep your gesso warm and handy. Pure hide glue based gesso will scorch and burn ... it doesn't smell good when it does.

Slaked plaster

Slaking plaster in period was a time consuming job. Gypsum or alabaster was roasted to make Gesso grosso (what we modernly call Plaster of Paris.) Gesso grosso was soaked in a bucket for a period of 1 month. During the tedious process, old water was drawn off, new water added and the mixture was stirred well and often. The plaster was considered slaked when the water remained clear. This process not only cleans impurities from the plaster, but adds an extra water molecule, or slakes it, so that it does not want to bind to itself. After reading and retranslating Cenniniís original text Jerry Tresser made this process a bit easier for modern scribes. He did many tests and found that you can slake plaster in 30 minutes rather than 30 days (Larger amounts of plaster require more time, but 4-5 cups of slaked plaster can be slaked in a couple of hours. That amount of slaked plaster will last most scribes several years.). Part of the time saved by using the modern process of slaking plaster has to do with starting out with a product that is more pure than its period counterpart. The rest has to do with realizing that unslaked plaster is acidic, slaked plaster is pH neutral.

To slake plaster in 30 minutes you will need:

Paster of Paris - about 1 cup
distilled water - a gallon is more than enough
litmus paper - 3 or 4 pieces
a bowl and spoon (I use plastic - disposable for easy clean up)

Test the distilled water with the litmus paper to make sure it is pH neutral. Place the Plaster of Paris in the bowl and cover with 3-4 cups of water. Stir well for 5 minutes then let the plaster settle to the bottom of the bowl. (Do not let the plaster sit in the bottom of the bowl without stirring for long periods of time. If the plaster is not completely slaked it will harden.) As soon as the plaster has settled, drain off the water, add fresh, stir well and let settle again. Repeat this 2-3 times then test the water. If the litmus paper reads neutral, you are done ... if not, repeat the process until the litmus paper gives the expected response. Once the water/plaster becomes pH neutral it is slaked. No matter how many times the mixture is stirred, the water is changed or how long the plaster soaks, it never gets any more slaked. Drain off as much water as possible, let the plaster dry in the bowl. You can store the dried plaster as a cake or grind it up and put it in a jar to store.

For further reading:

De Arte Illuminandi: The Technique of Manuscript Illumination. (1933).
(Daniel V. Thompson,trans.) New Haven and London: Yale University Press.

Grafe, Joyce. (1986). Secreta: Three Methods of Laying Gold Leaf.
New York: Taplinger Publishing Co. Inc. ISBN 0-87595-225-9

Thompson, Daniel V. (1956). The Materials and Techniques of Medieval Painting;
New York: Dover Publications. ISBN 0-486-20327-1

Tresser, Jerry. (1992). The Technique of Raised Gilding.
Port Jefferson, NY: Michelle Jordan Publications. ISBN 0-9633173-0-X

Copyright © 2006-2012 Maitresse Yvianne de Castel d'Avignon, OL (AEthelmearc)

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