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Water Gilding with Bole or Burnishing Clay

Water gilding is a technique for achieving a highly brilliant gild on wood. It is only for interior use.

Glue solutions

Glues are used to seal the absorbent underlying substrate. In theory, all animal based warm glues can be used. Bone glue has an advantage over the normally higher-quality rabbit skin glue, in that its lower gel-point allows for greater penetration. The recipe for glue size includes 1 part, by volume, glue to 6 parts water. The glue, whether hide-or bone-glue, must be soaked in cold water before being warmed. The glue solution should then be applied at 60o C.

Stone base

The stone base consists, as the name suggests, of stone chalk. An application of stone chalk gives firm and workable layers which both stabilize the surface and also, through their crystalline structure, form a good bond with the gesso to be applied later. The coats should not be too thick, as the stone base tends to form cracks. To make the stone base, use 3 parts by volume stone chalk and 1.5 parts water. This mixture should be left to soak overnight. The next day, pour off any standing water. Glue will again be needed as a binder. For this, rabbit skin glue is excellent. Bone glue should not be used here, because in high concentrations it becomes quite brittle. The mixing ratio for the glue should be 1 part, by volume, of glue to 1.5 parts water. This is left to rise overnight. The glue should have absorbed all the water. By warming over a double boiler to 60oC, the dissolved glue is obtained. This is mixed evenly with the chalk mixture. The stone base is then strained and is now ready for use. Due to its tendency to form cracks, the stone base should not be too thick. If needed, it can be thinned with diluted glue-solution. Dab on using a round bristle brush, taking care not to dab the same spot too often to keep the coat even, or twice in a row, in which case the first layer can crack as it dries. Keep the double boiler at 50 55o C. Stone base is sufficient when one even layer has been applied, but wood surface and contours are still visible. Generally 1 2 coats.

Gesso

The gesso base is the layered grounding for water gilding with bole. It is applied in layers and meant to conceal any irregularities and provide a pressure-resistant and polishable surface for later gilding. The gesso consists of the glue solution as well as various chalks.To make, use 1 part by volume rabbit skin glue and 4 parts water. The glue solution is made as previously described. As filler, you will need 1 part by volume of Bologna chalk, one part Champagne chalk and 1 part China Clay. The glue solution is placed in a bowl or pan, filling it halfway. The temperature should again be about 60oC. Sprinkle the chalks into the solution, rubbing through your fingers. Sprinkle one type of chalk at a time. The surface of the liquid should be just covered with chalk dust, which should sink to the bottom before the next addition. When lumps of chalk remain on the surface and do not sink, saturation has been reached. This time varies according to the types of chalk. Like the stone base, the gesso must be tho-roughly stirred and strained. The gesso is now dabbed on to the dry stone base surface in even but thin layers. It, too, must be warmed, keeping the double boiler no warmer than about 40o C to prevent formation of bubbles. After the second coat, the structure of the stone base and the wood should no longer be visible. Before applying the next coat, the previous one must be dry, at least on the surface. This means that no dark damp spots should be visible. To allow for possible repairs and the required sanding, you will need 4 6 coats. In the next stage, the gesso is thinned with maximum 5% alcohol, making it less viscous so it flows more easily. The alcohol has the advantage of evaporating without a trace and not changing the properties of the gesso. Thinning with glue solution would create too much surface tension. For the final base coats use a bole brush or a wide hair brush, (depending on the contours), drawing the brush evenly over the surface but no longer dabbing it. Finally, the surface should be sanded, either dry or wet. In wet sanding, use 360-grit sandpaper; in dry sanding 220-grit. You may also use pumice stone.

Keep in mind

As onerous as the sanding may seem, it must be done with the utmost thoroughness, as any tiny imperfections which remain will be even more visible after gilding. After sanding, be sure that the surface is free of any dust. This can be done by vacuuming or by wiping with a damp cloth. From this point on, avoid touching the piece.

 

Bole

The bole, or burnishing clay is applied over the gesso. Bole is actually the form taken by the clay once it is mixed with a glue. It can take two forms glue bole or egg bole. One thing is certain glue bole is easier to make and more durable, although egg bole is said to provide a more "fiery" gild. The first step is making the bole glue. Again, any animal glue can be used. In years past, the choice was the French sheets made by "Chardin". Today, however, German rabbit skin glue is at least as good, if not better. Rabbit skin glues, whether German or French, have the disadvantage of making the bole swell very strongly. Skin glue or gelatin have good properties. Alternatively, bone glue can also be used here. Hide glue is used in the preparation of our bole glues. In this case, quantities are given by weights and milliliters, as this is more exact than volume measurements. Mix 7 8 grams of hide glue with 250 ml of water. Let it soak and warm it to a liquid mass. The consistency is right when the mass is gelatinous when cold. Now the bole mixture can be made. For this two types of clay are needed. Begin with yellow clay. For 50 gr. glue mixture, you will need 15 gr. clay. Apply two coats. For a highly brilliant gild, then take red bole, using 20 gr.clay to 50 gr. glue (pigment is weaker). The glue should be only lukewarm but flowing, and is added little by little. Finally, the bole is strained and is then ready to use. Egg bole requires a great deal of preparation time. For 25 gr. of clay, you will need 30 gr. egg white (about one egg). The yolk is carefully separated from the white and the white beaten to a foam, which is then left overnight. This results in a clear liquid which is no longer gelatinous. Then the egg white is carefully stirred with the bole, strained, and placed in a closed glass jar. If left at room temperature, it will be ready in about two to three weeks; if refrigerated, wait four weeks. After preparation of the bole, the piece must be treated with a "blotting" coat. For this, use bole glue thinned with 1/3 water. This liquid is brushed on the gesso after being warmed to about 35oC. Do not make it warmer, or the gesso will dissolve, nor colder, or it wont penetrate the gesso. The purpose here is to seal the relatively absorbent gesso, but not completely, as the bond with the bole must be assured. Now you can begin laying the bole. Start with the yellow. The temperature should be a little below that of the blotting coat. Two coats of yellow are followed by two of red. If needed, the coat should be sanded. In the best case, brushing off with a bole brush is enough. For large flat surfaces, you can use 000 steel wool. It is important to clean off any dust from the surface to be gilded with a cloth afterwards.

Gilding

The piece has now been properly prepared so that the actual gilding can begin. As with all other methods of gilding, an adhesive is needed here. But unlike other gilding, in which an adhesive is introduced, here it is already contained in the glue component of the bole and must be reactivated with the help of a solvent. This solvent is a mixture of water and alcohol. The Special Solvent offered by Wasner Blattgold is one to which, a small amount of glue has been added, with the advantage that it lasts longer and does not dry out so quickly. This is especially helpful for less experienced gilders. The gild must be "floating". For this reason, wet an area no larger than the piece of gold which is to be laid. The gold must be laid onto the wet solvent. If the solvent has dried, so that the base shows only damp spots, it must be re-wet. Burnishing of the leaf may be started once the solvent has evaporated without a trace or has been absorbed by the base. In general, this takes two to three hours, but is of course dependent on room temperature and humidity. After burnishing, the gild is basically ready. If the piece is not subject to frequent handling or touching, it can be left uncoated. For objects which are to be handled, an overcoat is recommended. This can be either shellac or nitrocellulose lacquer. Gilding with white gold or silver must always be overcoated to prevent oxydation.

Please note:

Product-information and advice are given to the best of our knowledge and on the basis of our experience and testing. Such information, however, is not binding and excludes any liability on our part, regardless of whether the information was given verbally or in writing. Such information and advice are to be considered suggestions, which do not release the customer from the necessity of performing his own tests, in order to assure the suitability of the products to particular conditions. We also exclude any liability for damages which may arise from improper or negligent use of our items. The observance and carrying out of safety precautions and applicable legal regulations is the exclusive responsibility of the customer.