Traditional Water Gilding for Interior Applications

By Jim Hingst

Ever since hurricane Katrina battered New Orleans to a pulp in 2005, the Society of Gilders (SOG) has donated their time and materials to restore damaged gilded icons at two churches, St. Alphonsus and St. Mary’s Assumption. Originally decorated by European artists and craftsmen, the interior décor of these two pre-Civil War churches rivals the splendor and majesty of Europe's finest churches.

In late October of 2010, I joined several sign makers, artists, picture frame gilders and antique furniture restorers from around the country in this charitable effort. While considerable progress in the restoration was accomplished, the work of the gilders is far from complete.

Working with gilders from other segments of this field, also gave us the opportunity to learn new skills. Although many of my colleagues from the sign industry have considerable expertise in oil gilding exterior signage and water gilding glass, very few had ever attempted traditional water gilding using gesso and clay bole.

In the traditional water gilding technique, a wood frame or a wood carving is covered with layers of gesso and clay bole. After the bole is applied, its surface is rewet with what is called gilder’s liquor, and gold is applied onto the object. The final step in this time-consuming process is burnishing or polishing the gilded surface to a brilliant finish.

Because of the additional labor and material involved in this craft, water gilding is much more expensive that oil gilding. The quality of the gild is worth the additional expense, if you value the most brilliant, most highly polished gild possible.

Generally water gilding is used in interior applications to apply gold to wooden objects. Today this method is commonly used in refurbishing picture frames, carved statues, and to adorn furniture.

Some woods are well-suited for water gilding; others are not and should be avoided. If you do any wood carving, you’re probably very familiar with basswood. This is a very soft wood, with a very fine grain providing a smooth finished surface, after it’s sanded with a fine grit paper.

Typically basswood also doesn’t contain oils, which can bleed through the layers of gesso and bole, discoloring the gild. Woods such as pine contain oils, which are very problematic and (for all practical purposes) make them unsuitable. Oils and sap in the wood, will not only bloom to the surface (discoloring the gold), but they can also cause the gesso to delaminate from the wood.

But done correctly, the gilded work of art assumes the appearance of a solid gold object.

Surface Preparation

The key to attaining the desired level of perfection is proper prior preparation. Prior to the application of gesso, you should fill any nail holes and dings in the wood. Jill London of the Society of Gilders, who teaches traditional water gilding, recommends Durham’s Rock Hard Water Putty. This is a gypsum-based powder, which is mixed with water and used as a wood filler. When the water putty hardens, it becomes “rock hard.” Work fast when using this product, because it cures in short order.

One reason that craftsmen swear by this product is that it bonds to wood like white on rice and doesn’t shrink—even years after it has been applied. This makes it perfect for filling holes, gouge marks, and cracks in picture frames and wood carvings.

When you work with Durham’s Water Putty, only mix a small amount that you use within five to ten minutes. Since the water putty will harden rock hard, you may want to mix it in a clean tin can that you can toss in the garbage when you’re done.

The directions on the can indicate that you should add one part of distilled water at room temperature to three parts of the powder. This will produce a putty with the consistency of bread dough. You can mix the water putty so that it is a little juicier—to the consistency of sour cream.

Whatever you do, don’t use hot water to mix up a batch of putty. The heat of the water will accelerate the curing time, resulting in the putty hardening, before you have a chance to use it.

And be sure to keep your greasy, grubby paws off of the wood or you could contaminate the surface, compromising the adhesion of the water putty to the substrate.

You can use a craft stick or putty knife to apply the putty or you can use your fingers. After you press the putty into the nail holes or cracks and crevices in the surface of the wood, wait about twenty to forty minutes for it to set up. Small nail holes, should be ready to sand within this time.

After filling in any holes, sand the wood with 150-grit sandpaper and wipe the surface clean with a tack cloth. While sanding smoothes the surface of the substrate, it also helps to raise the grain of the wood, which gives the substrate some tooth for the gesso to adhere to.

Sealing or Sizing the Wood

After sanding, brush on a thinned coating of the rabbit skin glue, at a ratio of 20 parts of water to 1 part RSG. (Note: To read about preparing Rabbit Skin Glue, see our next section.) Take one part of the 10:1 RSG and mix it with one part distilled water. This will give you a 20:1 RSG mixture.

Before dipping your brush in the RSG mixture, wet it and squeeze out the moisture between your thumb and forefinger. Don’t pull on the hairs of the brush, or you could pull them out.

Liberally coat the surface of the wood with the 20:1 mixture. This coating will raise the grain of the wood, giving it some texture for the glue to grab onto.

Some gilders will brush on a second thin layer of the 20:1 rabbit skin glue, applied about twenty minutes after the first coating. The application of the second coating of glue helps fill in some of the grain, if you’re working with open grained woods (such as oak and walnut). The light layers of glue also help bind the subsequent layers of gesso the wood. If you’re applying the glue to irregular crevices on the frame, a filbert may help getting into the tight spots.

Recipe for Rabbit Skin Glue

In its dry state rabbit skin glue is dehydrated glue. To rehydrate the glue you must add water at a ratio of 10 parts of water to 1 part glue. Below is the basic recipe that Jill London and many other gilders recommend:

* In a clean glass canning jar with a lid add 28 grams of rabbit skin granules or pellets by weight. (Note: 28 grams equals one ounce.)

* Add 10 ounces (or 1-1/2 cups by volume) of distilled water to the glue, and cover the jar to prevent any contamination.

* Wait at least two to three hours for the rabbit skin glue to absorb the water. Better yet, mix the RSG and water the day before you intend to use it and allow it to soak over night.

* Before heating the glue, strain the mixture using a kitchen strainer. No, you can't strain it until after you have heated it. It won't go through the fine strainer until it's heated.

* In a double boiler, heat the glue/water mixture to a temperature between 98.6°F and 110° F.

* Carefully monitor the temperature using a candy thermometer. You can also monitor the temperature of the water with your hand. The water should feel warm. If the water is too hot to put your hand in it, it’s too hot for the glue. Excessively high temperatures above 120˚F will destroy the adhesive properties of the glue.

* Continue to heat the glue until all of the granules have dissolved and disappear. If you overheat the glue, throw it away and start over.

(Note: You can store the 10:1 RSG mixture in a refrigerator for up to two weeks. After that, the glue will decompose and spoil.)

Gesso

As smooth as the carved wood surface may be, it most likely has tiny imperfections. Left uncorrected, any imperfections (regardless of size) will be magnified, after highly polished gold is applied. One function that the gesso serves is to fill in the chips, cracks, and other defects, providing a smooth surface for subsequent layers.

While gesso will fill in the pores on the surface of the wood, it does not seal the wood; rather it allows the wood to absorb and release humidity as the atmosphere changes. This lets the wood expand and contract naturally. (Note: Cracking of the gesso at the corner joints is common. For this reason, fabric material is often applied over the joints to prevent cracking.)

After the gesso is completely dry, apply the bole clay. The color of the clay is important, since real gold leaf is somewhat translucent. Yellow clay will enhance the true color of the gold. Red clay, on the other hand, will give the make the gold appear warmer.

The ratio of rabbit skin glue to whiting is critical in determining the hardness of the gesso. The more glue you add to the mixture, the harder the gesso will become. As you add more whiting, the gesso becomes softer. If the gesso is too soft, it can crumble under pressure. The harder the gesso is, the more brilliant the burnish can be.

So why not mix the strongest gesso you can? One problem is that the harder the gesso is, the more difficult and time-consuming it is to sand. Even worse, if the gesso is too hard, it can become brittle and potentially can crack.

The amount of water in the gesso mixture does not affect its hardness. It does, however, determine the viscosity of the gesso. Thin mixtures are easier to brush and yield a smoother finish surface with less brush marks. The disadvantage is that you’ll need to apply more layers of these thin coatings to achieve the desired thickness.

Thick mixtures require fewer layers of gesso. If the gesso is too thick, you’ll produce brush marks. If you see brush marks as you’re coating the gesso, thin the mixture with distilled water.

As mentioned earlier, coatings are applied wet on wet. Subsequent layers are applied to previous ones before the gesso dries. If the gesso dries before you coating the next layer, you can rewet or dampen the surface with a wet sponge.

Because the ratios of the various components are very important, follow any of the recipes to the letter when you are starting out. You can always vary the recipes, after you have experience under your belt.

When you’re mixing the components of the recipes all dry ingredients are measured by weight; all liquid ingredients are measured by volume. That means that you’ll need an accurate digital scale and graduated glass measuring cups.

The recipes below are adapted from An Introduction to Water Gilding by Marty Horowitz and Lou Tilmont, Second Edition. 2007. Their book is essential reading for anyone serious about water gilding.

Their recipe for Gesso is different than my recipe: I use one part glue to two parts chalk, and I don't have to change this regardless of where I am in the world. I wouldn't ever mix denatured alcohol or linseed oil in the formula.

* Remove the glue mixture in the above recipe from the double boiler. To this mixture gradually add 1-1/2 cups of whiting. To prevent lumps, use a flour sifter to add the whiting. By sifting the whiting you will prevent lumps.

* Using a wooden spoon, slowly stir the mixture until the ingredients are completely combined, taking care not to form bubbles. Bubbles in the mixture can result in pinholes in the gesso. Vigorous stirring as you’re heating the mixture will generate bubbles in the gesso. Bubbles in the mixture quite often result in pinholes after the gesso dries on the substrate. To prevent the creation of bubbles, gently stir the mixture.

* On top of the glue/whiting mixture, add one tablespoon of denatured alcohol and half a teaspoon of boiled linseed oil. Allow the glue/whiting mixture to rest for one hour. The alcohol and linseed oil will help dissipate any bubbles that have formed.

* After the resting period, strain the mixture twice through a paint strainer.

Hingst-WaterGilding-FrameIf you want to make sure that the gesso is neither too hard nor too soft, follow the recipe exactly. Will any one recipe be perfect for every working environment? Probably not. Differences in humidity and shop temperature may require that you modify the recipe to satisfy your unique requirements.

Apply the gesso while it’s still warm. This will ensure good flow-out. If you’re applying the mixture to the intricately carved detail, you’ll want to use a stiff bristle brush; on the other hand, you should use a sable brush or a quill to apply the gesso to the flat smooth surfaces of your carving or frame.

In applying the first couple of coatings, brush a thick coating of the gesso—but not too thick to allow the gesso to puddle in the crevices. Typically six to eight coatings of gesso are applied. After you apply the initial coating, apply each subsequent coating before the previous coating is completely dry to ensure good intercoat adhesion.

Sanding the Gesso

After coating the wood with gesso and allowing to it dry thoroughly, sand it with 400-grit wet/dry sandpaper. Any imperfections in the surface will often result in imperfections in the subsequent layers of clay. In turn, these imperfections will glaringly show up when you lay the leaf.

When finished, the surface should be smooth as silk. Rub your fingers over the sanded gesso to find any rough spots. Also look for any other defects, such as pinholes.

After several coatings of gesso are applied, coat several layers of bole onto the substrate. When you’re finished, the surface should be as smooth as silk.

Carefully inspect the surface for any imperfections. Because your sense of touch is much more acute than your eyesight, rub your fingers over the sanded gesso to find any rough spots. Also look for any other defects (such as pinholes).

Bole

After several coatings of gesso have been applied, several layers of bole are coated onto the substrate. Bole is available in a variety of colors (including yellow, red, green, blue, black, and grey). You can also mix different colors of clay to create your own colors.

Bole is available as either dry cone clay or as a wet medium. The recipe below uses the wet clay:

Combine the following ingredients:

* 1 Tablespoon of wet clay medium

* 3 Tablespoons of distilled water

* 2 Tablespoons of 10:1 RSG

Thoroughly mix the ingredients until the clay has dissolved. Then strain the bole through a sieve to catch any lumps.

While gesso is a very thick coating that’s applied wet on wet, the bole is a very thin, water mixture that’s applied wet on dry. If you lay on the bole before the previous coating is completely dry, the thick deposit of wet clay could mud crack after it dries.

Hingst-Water-Gilding-01Water Gilding

Applying the multiple layers of gesso and bole is time-consuming, but the process isn’t difficult to learn. The tricky part is laying the leaf. While there are several different types of gold leaf, your best choice for traditional water gilding is 23k leaf. In gilding, you’ll need to cut the gold leaf into workable pieces. Check you gilder’s knife for any burrs that could snag the leaf. Then, using alcohol, wipe the blade clean of any oils.

Beginning at the back of the book, place a piece of matte board behind the rouge paper supporting the last sheet of gold leaf in the book. Then cut the gold leaf to the size needed with your knife.

To reactivate the rabbit skin glue in the bole, wet the surface with gilder’s liquor, brushing the area several times.

With the surface wet, transfer the leaf with your gilder’s tip. To pick up the piece of gold, charge your gilder’s tip with the skin oils of your face. Then lay the tip of the hairs of the brush on the piece of gold. Wiggling the gilder’s tip slightly from side to side can help secure the leaf to the brush hairs.

You’ll remember that I intimated that this process takes a little dexterity. The snapping motion of your wrist that you’ll have to master approximates a swinging door.

Did you see the movie Hitch? The kissing lesson that Hitch (Will Smith) teaches Albert (Kevin James) best describes the how you should lay leaf. If you’re going to kiss your date, Smith tells James to go 90 percent of the distance and let her go the remaining 10 percent.

The same advice applies to water gilding. Swing the tip of the brush almost all the way to the wet surface. As the gold on the gilder’s tip comes close to the wet surface, the water will attract the leaf for a clean transfer. At least, that’s the way the process is supposed to work.

In the real world, the gold will occasionally transfer with rips in the leaf. Not to worry. Just cut a piece of gold and apply it over the rip.

Surface Finishes

When you’ve finished burnishing, the gilded object should look like a solid gold! But after all the effort that goes into making something absolutely brilliant, why would you want to distress or antique it? In some cases, that’s exactly the look that people want to achieve.

In less extreme cases, you may want to simply tone down the brilliance of the gild in some areas to add some shading. Or you can use a mixture of Burnt Umber and Burnt Sienna Japan paints, thinned with turpentine, to shade the gilded pieces and wiping off the excess until the desired look is achieved.

In our restoration of carved panels in the communion rail at the Church of St. Alphonsus, we had the opportunity to do some toning. Using a mixture of Burnt Umber and Burnt Sienna Japan paints (thinned with turpentine), we shaded the gilded pieces.   The process involved wiping the surface with the mixture and wiping off the excess until we achieved the desired look.

Conclusion

If you want to accelerate your learning curve, you can also take a course. The Society of Gilders offers a course on traditional water gilding, as well as courses on many other gilding techniques.

Last year, classes were held in New Orleans concurrently with the restoration and regilding project at St. Alphonsus Church and St. Mary If you are interested in learning more about gilding and when classes are available, visit www.societyofgilders.org.

Sign makers are also welcome to participate in the New Orleans community projects, whether you’re an experienced gilder or a newbie (and whether you’re a SOG member or not). Last year, we accomplished a modest but beautiful bit of restoration. But much more needs to be done.

Please join us in doing something good for a community in need. It will be time well spent with other professionals and a chance to further your gilding knowledge.

For more information on this year’s restoration projects in New Orleans, contact Dr. Francis Lestingi at Francis@SignsOfGold.com.


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