Mica powder is a pigment used in a binder like varnish or shellac to create metallic finishes. The advantage mica has over metal flakes is it's inability to tarnish. By creating your own metallic paints you are able to dictate the color and choose a binder that is suitable to the job you have on hand. By choosing a binder that does not yellow with time you can have a surface coating who's life span exceeds today's standards.

To create mica powders the stone, mica, is ground. Mica cannot tarnish since it is not metal. It grows in a layered structure, kind of like an onion, and has a mother of pearl translucency. This is what gives mica powder it's fantastic reflective quality.

When these mica platelets are ground they create a particle that is many faceted. Bronze powder, the metallic pigment of choice in the past, is basically a two faceted flake of metal. Being metal, bronze powder has all of the oxidizing properties of bronze itself. These pigments are usually stable until the protective coatings are worn off or the metal content of the coating chemically reacts with the binder. Since mica is an inert rock it does not chemically react with any binder during or after application.

When color matching is an issue micas are helpful because they come in over 35 colors. Shades of gold, copper, silver, pewter, mother of pearl with red, blue or violet hi-lites and hornet blue/green. To achieve this the mica powder is treated with titanium dioxide and/or ferris oxide. This treatment does not make the powders chemically reactive in any way. As with all pigment the size of the particle of color is important and with some micas there is a choice between regular and micro which is extra finely ground. An external mica is also available in some colors and this particle is larger than regular.

Micas can be mixed together for creativity and precision when matching and creating coatings. In the past mixing your own metallic coatings was hazardous because airborne metallic powders are very toxic. There is no such hazard with mica powder. The airborne particle is an inert rock instead of a flake of metal.

It is important to note that when touching up or color matching there will always be a significant difference between any gold pigment and leaves of gold. When light hits a piece of metal leaf, gold or other, the light is reflected off of a single reflecting plain. When light hits a gold pigmented surface the light is reflected off of many different reflecting facets. This makes metallic paints grainy next to the way light can travel on the surface of a metal leaf.

So why bother if it is not good enough? Well, because sometimes we have to and we can. Micas mix easily by the brush stroke or by the batch. This could be more economical then releafing. The effects of graininess are not always visible from a distance. Touch-ups in pigment could be restricted to shadowed or dark areas and leafing only the highlights. Matte gilding can sometimes be grainier than a finely pigmented, gold paint.

For restoration the advantage to mixing your own touch-up medium is that you can insure easy removal when the time comes for a complete overhaul. You should choose you binder accordingly. Should you get the big renovation job and it is to be done with conservatorial considerations, you will be glad you were the one caring for it previously. You will be able to remove old repairs with ease and without damaging the original gilding.

All surface coatings are a mixture of a binder and pigment which means that mica is great for any type of surface coating you need to have. Micas can also be brushed onto a surface that has been coated with a binder instead of mixing the binder and pigment before application. This makes for a more opaque and even surface. The pigment adheres to the surface of the binder. There is no need to seal this surface though one could. The binders of choice for this technique are the traditional linseed oil gilding size or the modern water based acrylic gilding sizes. These sizes can also be pigmented with tinting pastes exploding creative possibilities.

Micas powders are not new. They are in cosmetics, automotive paints and plastics to mention a few. It is their use in decorative painting and gilding that is revolutionary.

Grace Baggot

August 98'