Applying liquid gold, palladium and/or silver in the final firing of enamel pieces is something that can frequently raise the appearance of a completed piece up to the spectacular. More enamelers should use them, but they should also learn to use them correctly. If they adhere to the following simple suggestions and procedures we feel that greater success will be achieved in their use.
When applying and firing a layer of precious metal it is advantageous for the artist to have a real conceptual knowledge of just exactly what is it they are doing. During the actual enameling steps of their project they have taken granules of glass and fused this sandy material onto a metal substrate to form a continuous glass surface which may be from one to four hundreds of an inch thick.
Although this may sound like a very thin layer it is a thick enormous mountain range when compared to that which one achieves with precious metals. Here the thickness required to produce a solid appearing metallic surface can range from that of a few molecules to no more than a few millionths of an inch. Putting down a second or third coat to cover a bump or fill a scratch will be about as effectual as a second or third light dusting of snow to make the Rockies disappear or fill up the Grand Canyon.
In the enameling firing step, quite a bit of glass movement occurs in smoothing out the glass. In the precious metal firing, solvents and organic materials burn off leaving pure metal bonded to the glass surface. Virtually no helpful material movement occurs. What you start out with is what you end up with, and no additional firing will improve this condition. If the surface has scratches, pinholes or bumps, the metal coating will highlight and emphasize them. If a crack in the metal coating occurs on firing, refiring will not heal it. The only defect correction that can be made is when the metal coat has been applied too thin in spots. This defect can be covered with a second coat and the piece refired. The goal then is to get the metal down correctly in the first place and then fire it in such a manner that the uniform surface is not destroyed. When this is done, a beautiful metal surface always results.
Enamel preparation involves two subjects, surface texture and surface cleanliness.
The reflected light off a metal surface is a formidable one. It doesn’t hold back its punches. It shows you everything that’s there. This is why if you want a truly smooth surface free of scratches and bumps you must make it that way. The metal will not cover them up. It will highlight them. Consequently, stone the surface smooth with a 220 grit stone, followed by final polish firing.
The proof is in the pudding. If you want to see the problems a dirty, greasy surface can cause, try brushing liquid metal across a great big thumb print you have deliberately made on an enamel surface. Good luck! Clean your piece well in mild detergent and water solution prior to applying the liquid metal. Some enamelers go one step further. They heat the enamel up to about 800oF in their enameling furnace, (about one minute for one set at 1450oF), and immediately do their metal application after the piece has cooled.
A very smooth, clean enamel surface works quite well if you are applying metal with a brush. When you are applying fine lines with a crow quill or ruling pen it helps to have a “super” smooth enamel surface. This can be achieved by further polishing the smoothened surface under running water with ultra fine wet//dry 400 grit paper. This you can purchase at most hardware stores. Again the piece is polish fired at 1450oF. If your piece is not used for a day or two, repeat the washing and 800oF fire so that the surface is just right.
Nothing is more important in applying an even, uniform area of liquid metal onto a properly prepared enamel surface than quality of the brush or pen used to apply it. Nothing! They, too, must be cleaned, preferably being washed in the solvent essence of the metal.
Bands or areas should be put down using a quality sable shader, and lines can be drawn using a fine point sable. Thickness of metal or paint put down by any brush is directly related to the diameter of its hairs or bristles. With metal application, the deposit must be uniform and as thin as possible, just thick enough in fact that a metal surface will appear on firing. The thicker you apply these metals the more trouble you are bound to have on firing. This is a classic case where if little is good…more is worse!
Learning how thin to apply can only be done with practice. A good way is to draw successive short bands with a brush until the brush runs dry. Look at the condition of the bands prior to firing, fire and examine the results. We feel many enamelers will be amazed at how good a very thin deposit will turn out, In using liquid metals, enamels have one real advantage over pottery, they can quickly be refired. You do not have to wait for a firing that can take a whole day. There is nothing to be gained by loading liquid metals on but trouble.
Get familiar with the brushing consistency of liquid metals as you receive them. This viscosity or paintability is very important. Thin only when it is physically apparent that brushing is difficult and then thin sparingly. You are painting with a carefully prepared blend of solvents, organic vehicle and metal particles. Excessive thinning will cause the metal to float and brush streaks will occur. Some of these will fire out, but some will not.
The use of crow quill pens or drawing pens takes practice even if you are drawing with India ink. Don’t think you can write a good signature or design the first time you try. Practice! Practice! Practice! Become a self-teaching detective, look carefully at what you have drawn. Remember or sketch down what you are dubious about being right. Fire the test sample and compare the fired results to the prefired surface condition. Keep a notebook. This is the best way to keep from reinventing the wheel each time you use liquid metals.
A final suggestion in applying liquid metal is don’t be shy about using a guide bar or a crutch in drawing lines or letters, the best sign makers do and they really give added control in taking the shakes out of drawing. They will make you look like the real pro you wish you were. Create one, such as that shown in Fig. 1, with spacers and a ruler. Make it fit your own manner of holding a brush or pen. These guides also help protect the clean enamel surface from needless fingerprints.
Once an even, uniform surface has been achieved, the goal becomes keeping it that way until the firing process is complete. Prevention of any break up begins first with carefully drying off the liquid volatiles, usually toluene, chloroform and cyclohexanol. Next, the organic materials which provide the brushability of the paint by keeping the metal particles separated and suspended must be removed. Finally, the precious metals along with their fluxes need to be bonded to one another and onto the enamel surface.
If your enameling furnace is at room temperature, load the piece to be fired, keep the door slightly ajar, and turn the power on to low. Let the furnace naturally and slowly heat up to about 800oF. During this time you can look into the chamber and watch organics sublime or burn away. You are never ready to proceed further with the firing process until it is evident that all activity of this type has ceased.
If the enameling furnace you wish to use is already on and up to normal enameling temperatures, turn it off and open the door. Keep an eye on the furnace’s pyrometer and only load your ware after it reads less than 500?F. At this time turn the furnace on to low and proceed back up to 800oF.
After you are certain that volatiles and combustibles have been removed, all that needs to be done is the final firing step. It is different than if you are firing onto fine China. This difference concerns the softening temperature of the glaze as compared to the enamel. An enamel will begin to soften at a much lower temperature. In fact, it is right down in the maturing range of the precious metals. Consequently, extra care must be taken not over fire or to fire too long. If these errors are not avoided, cracking and break-up as seen in Fig. 4 and Fig. 5 will occur.
Proceed by closing the furnace door and turning the power up to high. When 1250oF has been reached, start checking into the chamber and watch for the moment the metal surface appearance changes from a dull, dark matt to one of a real metallic sheen. When this occurs, fire no longer than two to three minutes more. Remove the enamel from the furnace and allow it to cool to room temperature.
As with all procedures which can vary when you attempt to repeat them off-the-cuff, keep a note book so you don’t have to. Metallic surfaces can look well fired and still not be bonded to the enamel. An excellent way to check for underfiring is to rub the metal area with a soft pencil eraser. If break-up occurs, re-apply a second metallic coat and refire; this time extending the final soaking period. Jot down the successful soak period in your note book.
Remember as basics these three points:
- Paint thinly and only on very clean smooth surfaces.
- Carefully burn off volatiles and organics.
- Fire at 1250?F and only as long enough as necessary to get a bright metallic look which is well bonded to the enamel surface.