Enameling has existed for millennia, responsible for much fine art. Enameling is the process of fusing colored glass with metals, and many elements contribute to the look of the finished product. Gold, silver, and copper provide the best metal bases, and different firing temperatures and times change the enamel's appearance from reflective to glossy to gritty. Finally, a myriad of enamels are available with different colors and qualities. Oxides within finely ground silicon produce the color of the enamel, and the concentration of oxides creates opaque or translucent qualities.
This experiment will primarily test the effects different firing times have on the appearance, texture, and color of opaque and translucent enamel. Three rounds of test strips will be fired at different temperatures for thirty seconds each. Each round will contain two test strips: one of strips will be coated with opaque enamel and one with transparent enamel, and the firing will be first in the lower temperature range for firing enamel, the second in the middle, and the third in the upper.
The different firing heats should produce significantly different colors. Higher heats should cause the colors to grow darker in value and redder in hue, yet saturation should not be significantly affected. Transparent and opaque enamels should change color at similar rates, but their colors should differ. Transparent metals should be fully fired to become truly transparent or glossy. Finally, an underlying base should significantly impact the actual color of transparent enamel.
|The temperature of the kiln||The size of the copper strip|
|The copper, flux, and opaque white enamel bases used with the transparent enamel strips||The color, type, and concentration of the flux, counter-enamel, and base metal, and the transparent and opaque enamel.|
|The amount of enamel applied to each strip||The general firing and cooling time|
|Slight variations in firing and cooling times||The kiln used|
|The number of firings on each transparent strip (2)|
To prepare the base metal strips, copper is cut into rectangles of the same size approximately 3/4 of an inch wide by 1 and 1/2 inches long. The strips are cleaned thoroughly, dipped in an 3 M nitric acid bath and then scrubbed under running water with 00 steel wool. Gloves and goggles are used when handling the acid and in order to prevent oil from the artist's hands to tarnish the cleaned strips. While cleaning the copper, the kiln should be heating up.
To prepare the enamel, counter-enamel, and flux, their respective powders are mixed with a small amount of water in a small evaporating dish and continually rinsed and re-soaked until the water remains clear. At this point, all impurities have been removed from the powders.
Although the strips and enamel are prepared, before applying any enamel to a strip, counter-enamel is applied to the back of the strip. To apply any type of wet powder, a spatula is used to remove a blot of the wet powder from the evaporating dish. The flat end of the spatula is then used to spread the enamel in an even layer; once all the desired amount of powder has been applied, the strip is tapped lightly at the sides to smooth any uneven surfaces. The corner of a paper towel is applied to the corner of the strip so that it absorbs excess water. The strip is placed atop the kiln to allow the enamel powder to dry. The powder must be dry before firing.
The strip is fired at 1500 degrees Fahrenheit so that the counter enamel just sticks roughly ten seconds. Tongs are used to insert and remove the strip from the kiln; and the strip is placed on a small ceramic platform (a mesh screen is ideal). After firing, the strips are cooled on a graphite slab.
The enamel paint is applied in different sized strips according to whether the enamel is opaque or transparent. Thompson Enamels manufactured the enamels for this project, and sky blue constituted the color of both the opaque and transparent enamels.
|Under Firing||Moderate Firing||Over Firing|
|Appearance of Kiln||Dull red to dull orange-red||Cherry red to bright red orange||Very bright orange|
The copper strips, cut from a sheet of thin copper foil, were easy to size. The clean copper had a greater sheen and a soft orange color compared to the dull brown of the oxidized copper.
Cleaned copper strips versus oxidized
|The copper was very oxidized but easily cleaned after the acid bath. The copper did not bubble profusely in the acid. Not all oxidation was removed in the acid, but the steel wool quickly removed any remaining with light scrubbing. The steel wool left subtle streaks on the copper.||
Counter-enamel powder was much coarser than the enamel powders. It resembled beach sand, and had flecks of white, black, and blue; it ultimately appeared a dark navy color. A spatula was necessary for applying the counter-enamel and any other enamel powder to the copper. A paint brush absorbed much of the water and enamel and could not spread it flatly. It took the every powder a few minutes to dry completely atop the kiln. The strips had to be handled gently thereafter so as not disturbed the dry layer of powder.
The fired counter-enamel still held is freckled appearance, and was glossy and reflective.
|The counter-enamel needed just around ten seconds in the kiln at 1500 degrees to melt and fuse to the copper. Tongs proved to be the best instrument to for moving the copper strips in and out of the kiln; they offered more control than lifting the strips with a pallet knife. Firing the counter-enamel affected the copper; it became much darker with red dots and a smooth, piebald surface. Also the strips seemed to mold to whatever surface they were placed on; open spaces underneath and non symmetrical support caused the strips to warp. The counter-enamel sometimes melted onto the ceramic support in later firings, but it did not cause any significant problems. When it did melt, the counter-enamel would for a string of itself from the ceramic support to the strip. The thin strip hardened quickly and was as brittle as glass.||
The copper changed color after it was fired with the counter-enamel. The counter-enamel became highly reflective after firing but always remained the same general color.
Counter-enamel (left) and opaque sky blue powder (right). Wet enamel powders are darker than the same dry. The appearances of opaque and transparent enamel powder, wet and dry, do not differ significantly from each other.
Opaque enamels proved the easier to work with than transparent ones. All enamel powders were spread easily with the use of the spatula. Opaque enamel powder and fired enamel appeared sky blue. The base copper did not effect the fired enamels color although the high fired strip had a green tinge around the enamel. The high fired enamel looked thinner and smoother than the others and darker in color. The medium fired strip's surface was smooth and even and a true sky blue. The low fired strip had a surface gritty like an egg shell but did not differ in appearance from the medium fired enamel. The final strips and the temperatures under which they were fired are below.
Transparent enamel proved more difficult to control due to multiple firings for each strip. The flux was a clear, slightly grey powder with a similar coarseness as transparent and opaque enamel; the flux was rinsed and applied like any other enamel powder. Transparent enamel powder is opaque and almost identical in appearance to opaque powder.
First Firing: The three strips of applied enamel kept their boundaries well and did not bleed into each other although water did pass the registers. The opaque white undercoat enamel always stayed a clean white no matter the firing temperature. The flux and transparent enamel did not seem terribly different in appearance, yet the flux was more red and the transparent enamel more purple. The copper definitely affected the color of the transparent bands.
Second Firing: The transparent enamel was spread easily over the flux and the opaque white undercoat. The top layer of transparent enamel did not significantly affect the color of the flux, but did make it slightly more purple. A blue sheen can be seen when the strip is twisted under a light. The flux/enamel band is more blue than the enamel applied to the copper itself. The enamel on the white undercoat appeared sky blue and perfectly transparent under all firing temperatures. The temperature ranges did not change its color, nor the color of the band of transparent enamel that was directly applied to the copper. At higher temperatures, the upper layer of transparent enamel melted and bled over the strip, but the underlayers remained separate. With increased temperatures, the enamel directly over the copper and over flux appeared more red and less purple. At the high fired range, it appeared red orange. The final strips and the temperatures under which they were fired are below.
Two strips after the first firing. The strata involve opaque white enamel at the top, flux in the middle, and transparent sky blue enamel at the bottom.
My hypothesis that the different firing heats should produce significantly different colors proved false. Colors never changed significantly between fired enamel although fired enamel and enamel powder differed in appearance. The color of the powder is not a bold as fired enamel, which is also more reflective, and transparent enamel powder is opaque. Higher heats did not cause the color of the enamels to grow darker in value and redder in hue. Moreover, transparent and opaque enamels did not differ terribly in color, but greatly in texture and appearance. However, the hypothesis that an underlying base should significantly impact the actual color of transparent enamel was correct. The color of the copper mixes with and dominates the color of the transparent enamel and flux; however, the transparent enamel atop the opaque white base appears truly sky blue.
The experiment differed from the original plan in a few ways. I had never enameled before, and although I understood the basic process of enameling, I had to learn some of the finer techniques of the procedure, such as spreading enamel and finding the optimum firing time. Also, I learned which tools were better suited for the experiment. A spatula is necessary and tongs proved the most useful in handling the strips. I made a few mistakes, such as putting a strip in the kiln while the counter-enamel was still wet (the enamel literally exploded off of the strip). However, I had allotted time to tune my procedure and experiment with enamel so that I would not make mistakes when I created my final test strips. The results differed from what I expected, but the procedure differed little from the original plan.
Thompson Enamel Company
Chemistry and Art at the University of the South
Glass on Metal: The Enamelist's Magazine
Bates, Kenneth F. The Enamellist. Cleveland, World Publishing; 1967.
Franklin, Geoffery. Simple Enameling. New York, Watson-Guptil, 1971.
McGrath, Jinks. The Encyclopedia of Jewelry Making Techniques. Philadelphia, Running Press; 1995.
Dr. Bachman for the use of a smaller, more accurate kiln. Ms. Bachman for ordering supplies and more importantly, having them rush delivered. And of course, Dr, Bordley for help while I organized and executed the project.