My start with the lusters:
Being related to Louis Comfort Tiffany, I have carefully studied his interests and tried to compare them to my own at the time I started blowing glass (1987). As I saw it, there are many similarities, but there was one area that I thought that I would not want to touch: metallic lusters. Tiffany was fascinated by the effects of various metal salts sprayed on the surface of the hot glass creating a cloud of toxic fumes which coats the piece in a rainbow of colors. As I started blowing glass, I decided that, for health reasons, I would forego thinking of lusters as an available decoration.
Years later, I found pearlescent lusters. I started with a palette of three colors and was led to twenty-five. The more I used them the more I wanted to use more. Since about 1999, the majority of my work utilizes pearlescent lusters. I woke up one morning to realize that I was beset by the same intrigue with lusters as Tiffany; I had simply backed into a twenty-first century way of achieving a look that a century ago could only have been done using toxic fumes in the studio. The pearlescent lusters, on the other hand, are a good deal safer than most of the class colors used in the studio.
What are pearlescent lusters?
Pearlescent lusters are platelets of mica which have been coated with titanium oxide and/or iron oxide to give them a color. The color is an interference color. That means that some wavelengths (or colors) bounce off the surface better than others do. If the thickness of a coating is not well controlled, we see a rainbow of colors as in oil slicks and soap bubbles. In fumed glass and pearlescent powders, the thickness of the layer is constant enough to produce a hue to the surface. One color of light reflects off of the surface while its complimentary is transmitted through the platelet; thus it is dichroic. Layers such as these under high control, and in multiple layers, produce what most glass artists call dichroic glass.
The platelets of mica are in the range of 2-100microns. When attached to the surface of glass, they impart tiny facets which are not perfectly parallel to the over-all surface of the glass. Hence they blur the reflection such that a reflected point of light is seen as fuzzy ball. At first it might be thought that blurring such as this would decrease the information which we see from the surface. On the contrary, this blurring tells our eye more information because, from a single point of light, we get information about the region of the surface which is nearby the reflection of the point of light. When we take a picture of a piece of glass, we are interested in the surface contours of the glass, and not its reflection of the bright lights illuminating the glass. So, pearlescent surfaces provide more information about the surface than shiny smooth surfaces.
Because the platelets are flat, a point of light will be reflected at one angle. If the platelets are big enough, they sparkle. In part, we see this because one eye sees a reflection from a particular point and the other does not. Alternatively, as we move our eye [or move the piece of glass] slightly, illumination of a point on the surface changes. Our eyes [actually a lot of stuff behind our eyes] are programmed to have a great interest in such an effect because it is closely associated with movement in our vision, and movement out there is almost always more important than still objects. So, sparkling surfaces trick our eyes into being interested in the subject.
Finally, since the mica platelets have a color, we can create surfaces where background color of the glass is different from the reflection from the luster. And, by putting down a luster on the inside of a vessel, that surface can be visualized as a color. (Normally the inside surface of a vessel is not interesting or noticed.) The result is an object whose color is hard to define: it doesn’t seem right to say a color is gold and red and blue all at the same time, but with lusters on glass it makes sense. All of these effects are incorporated into these tiny reflective plates when put on the surface of glass. That these pearlescent lusters wow the senses and lure the attention of the observer is attested by their major commercial uses: First, these lusters are responsible for the myriad of “metallic” finishes seen on those shinny new cars. Secondly, these lusters are the same that are seen decorating the eyes, faces, and lips of women. And finally, the lusters are used in the decoration of fish lures.
How to use pearlescent lusters:
It is simple: the mica platelets stick to hot glass. The easiest way to coat a vessel is to roll the piece in a stainless steel bowl containing the luster. For even coating, a sizable excess of the luster is necessary; I routinely use a 9-12 in bowl and about a pound of the luster. A pound of luster goes a long, long way. Since encasing the lusters destroys most of their effect, the right time to roll is after the last gather. Once the surface has been covered, it will stick no more: an even coating is easy because the density of the luster is self-limiting. The drawback, though, is that the surface does not want to accept more hot glass. These lusters are not good for bit work and there are sometimes problems with punties. A hot punty will often work, especially if the piece has been inflated after being coated. For larger pieces, I use button before puntying.
To coat the inside surface, I put several teaspoons of a luster inside the vessel as I am starting to open the neck. To attach the lusters it is necessary to heat the whole piece to where it begins to move. The excess luster is poured out so that it doesn’t spill.
Special effects can be had by rolling the piece in luster when the piece has formed a skin. The luster will coat the surface, but it is labile. A rolled-up “newspaper pencil” can be used to draw on the surface by wiping off areas of the luster. Similarly, if the piece has crevasses, the high regions can be wiped clean of the luster leaving the crevasses with the luster color.
The luster may be spread on a rough marver. If the piece has ripples or has been in a blowing mold, the highlight of the surface may be coated with luster while sparing the valleys. I have found that silicon carbide kiln shelf works particularly well for this.
These lusters may also be used with slumped glass. I have found it convenient to paint it on in a weak solution of gum arabic. If too thick a coat is applied, all of the luster flakes off, leaving a hole in the color.
Clean up of pearlescent lusters is particularly important if you are renting or sharing a studio. The versatility of the lusters makes them the tool of choice for many effects but their careless use will rapidly result in blanket edicts forbidding their use. OSHA categorizes the pearlescent mica lusters as a nuisance dust, but their flashy color catches the eye in the buckets and on the floor far more than the relatively invisible but far more insidiously toxic color powders. As usual, the key to cleaning up is to minimize messing up. With a particle size of two to tens of microns, they can remain in the air for some time. Care in handling them starts with avoiding kicking up a lot of the dust in transfer from one container to another.
Spills do occur and it is useful to have the spill occur upon something disposable. I have found that a wetted sheet of newspaper on the tool-shelf of the blowing bench and on the floor next to the bench and below the piece being worked works well. The lusters are quite hydrophilic [that is, they wet easily] and if the newspaper is wet, the lusters will tend to stay with the newspaper, even after it dries out. Spills on the floor of the studio create tracks which will last for days under normal wear and tear. Avoid walking on them and when the piece is finished, vacuum the spill up. A shop-vac works well for this. Residue on tools can be washed away. Wood blocks represent a squeaky wheel of the process. Although a wet block cools a gather of glass down to the point that lusters on the block will not stick and contaminate the glass, owners and proprietors of such blocks view with some concern blocks left with a pink or gold tint upon them. Indeed, there is usually no reason to use the blocks after coating a piece with lusters.
These pearlescent lusters are a useful compliment to the more normally used elemental pigments for glassblowing. They are available in over a hundred different colors and add the design choices in glass colors. I feel that their utility has yet to be tapped by the glass community. They sparkle, they dazzle, and they add depth to the surface which is not available by any other technique.
By Rodman G. Miller
written in 2004, revised July, 2012