The etymology of the well-known in the West “ mordant technique ” , also known in our country as mixion, is related to the property of certain materials to stick to the touch before they are completely dry. (from Latin: mordere – I’m munching). There are two types of mixtures onto which the gold leaf is applied and adhered: polymer-based and oil-based.
Gold plating with a polymer-based mixion
Polymer Mixion is an aqueous dispersion of vinyl and/or acrylic polymers. It is the easiest alternative for applying slag metal and is particularly suitable for porous surfaces.
Preparing the Base
The quality of the gold plating depends largely on the careful preparation of the substrate. After thorough preliminary cleaning (dust removal and degreasing) appropriate to the type of surface to be gilded , several layers of a suitable primer are applied to it.
In most cases, the primers used for gilding contain a finely ground filler (wienerweiss, chalk, or slaked gypsum) and an aqueous solution of animal collagen (rabbit, fish, calf skin glue, or gelatin).
Once the surface has dried, it should be sanded (using fine-grit sandpaper to remove any unevenness) and dusted off. To visually conceal any cracks and minor defects in the gilding, a coat of acrylic paint in a suitable color can be applied over the well-smoothed primer.
Next , apply the mixture with the utmost care—quickly, thinly, and evenly (using a well-wrung brush, without repeatedly going over the same spot or rubbing it in).
The polymer-based bonding agent has the advantage of reaching its bonding stage extremely quickly (15–20 min) and retaining its bonding properties (open time) for more than 24 hours.
Gold Plating
Once we have waited the necessary time for the Mixion to cure, we proceed to apply the metal leaves, deciding whether to use them whole or to cut them to the appropriate size. Depending on the surface area and texture, we can use various tools: a sheet of paper or a special gilding brush, which we periodically electrify so that the gold leaf adheres to it.
When laying the sheets, we make sure that each subsequent sheet overlaps the previous one by 1–2 mm and does not get crumpled. Once the entire surface is completely covered with metal sheets (slag metal), we begin to gently press and smooth them with a soft brush. Powder and blush brushes, for example, prove to be very useful for this purpose.
Cleaning the Gilding
Using a softer brush, we remove any excess pieces of metal leaf that have not adhered to the surface. When gilding with polymer-based gilding paste , this can be done immediately after gilding.
The final matte finish achieved with this gilding technique pales in comparison to the luster offered by oil-based gilding, and is incomparably far from the impressive capabilities of ancient water-based gilding.
Varnishing
The finished gilding, filled with slag metal, copper, aluminum or silver, must be varnished to avoid its oxidation. The traditional and most reliable varnish coating is the alcohol solution of shellac , but nitrocellulose varnish can be used, as well as some acrylic varnishes.
Gluing with an oil-based adhesive
Oil-based mixes contain partially polymerized boiled linseed oil and resins; depending on their proportions, they have different open times—3, 6, 12, or 24 hours.
The oil-based mixture is particularly suitable for application on non-absorbent surfaces. It allows us to gild glass, metal, and ceramics.
For absorbent surfaces such as wood, plaster, and stone, it is recommended that they be primed and varnished beforehand to seal the pores of the material they are made of.
Because of its relatively longer drying time, oil-based paint can be applied extremely thinly and evenly. This, in turn, highlights both the characteristics of the prepared surface (texture, engraving) and any potential defects.
That is why we must take extreme care when preparing the surface to be gilded. The principle of applying gold or metal leaf is the same as for gilding with a polymer-based gilding paste. Unlike that method, however , when using an oil-based mixture, we must wait 12 to 24 hours before cleaning it. Our patience will be rewarded with an exceptionally smooth and shiny surface.
The advantages of oil-based gilding are that it can be applied to various surfaces and allows for the use of any type of metal sheet: karat gold (gold leaf), sterling silver, brass (slag metal), bronze, tin, and aluminum.
Items gilded with oil-based mixion and further protected with a suitable UV-protective varnish are not affected by weather conditions and can be displayed outdoors. Oil-based mixion gilding does not allow for polishing of the metal surface. No matter how well it is applied, it cannot compete with the mirror-like effect offered by polished poliment gilding.
Water gilding
Water gilding, also known as “poliment,” is the oldest technique for gilding with gold leaf.
Historically, it has been used in most of the works of fine and applied art known to us. The process is much slower, more labor-intensive, and more complex.
The technique of water gilding is an art that requires a high level of practical skill and in-depth technical knowledge, so the quality of the final result is determined by personal experience and sustained practice, rather than solely by the application of a specific formula.
There are certain recommended proportions for the quantities of the ingredients in the polish. However, their precise calibration must take into account a number of additional factors, such as temperature, humidity, air circulation, surface texture, and surface area. Small changes in the proportions lead to significant changes in the quality of the final result.
Only experience, combined with in-depth knowledge, can foster the sensitivity needed to achieve a perfect result.
This gilding technique is known as “water gilding” because the gold is fixed to the surface by activating the “adhesive” contained in the ground through wetting. The poliment is the coating applied over the primer that allows the gold leaf to adhere firmly and makes it possible to polish it. It acts as a flexible bond between the prepared surface and the metal leaf.
The poliment contains bolus (a fine clay composed of iron oxide, calcium and magnesium silicates in varying proportions) and a protein-based binder of animal origin (egg white, gelatin, rabbit glue). The color of the poliment (brick red, ochre, or black) depends on the proportions of the individual components in the bolus.
The water gilding technique, which allows for the polishing of gilded surfaces, produces a result identical to that of solid gold, with its characteristic dazzling luster.
Preparing the Base
Several layers of gesso are applied to the prepared surface (primed, smoothed, and polished), each of which is also smoothed, dusted, and polished with a special brush.
Gold Plating
The dried gilding is activated by moistening it with what is known as “gilder’s liqueur” (a very dilute solution of gelatin in water, to which a small amount of alcohol has been added).
Immediately after wetting the area of the surface (slightly larger than the size of the gold leaf we are about to apply), we place the leaf using a special brush. Next, wet the adjacent area, apply the next gold leaf so that it overlaps the previous one, and continue in this manner until the entire surface is gilded.
Next, use a soft brush to smooth out the gilding in the direction of the overlapping sheets. Then, using the same soft brush, carefully remove any excess gold flakes.
Polishing
Polishing should be done before the polish has completely dried. We determine the right time to polish by gently tapping the surface with an agate (a polishing tool) and testing a small area. A sense of the sound that indicates the optimal moment comes with experience. The agate should not scratch the gold but should glide smoothly across the surface.
Once we’re done polishing, we correct any defects (cracks or areas where the material hasn’t adhered), which we then polish again as well.
Varnishing
Once we are satisfied with the result—a dazzling mirror-like shine— the gilding can be protected with a suitable varnish: shellac, damar varnish, mastic varnish, or acrylic varnish.
Further processing
If desired , various techniques can be applied to alter the final aesthetic result: patination , rubbing, toning, sgraffito (probaster), embossing, and others.
The publication of this series of brief technical and technological guides, based on knowledge and many years of practical experience, is an effort to preserve and carry on this ancient tradition.
By helping beginners in this challenging field, to use both traditional and contemporary techniques and materials competently and correctly, and to help viewers develop the ability to evaluate the results achieved by contemporary gilders, we hope that the ancient art of gilding will continue to thrive.
Authors: Radoslav Hristov and Assoc. Prof. Svetozara Georgieva Ratsova-Hristova, Ph.D.
