Think you don't have bubbles in your enamel? Think again. Pretty much all enamels contain bubbles to some extent. They might be so small you can't see them without magnification, but trust me, they're there. And they are clouding up your gorgeous transparent enamels.
There are a number of things that cause bubbles, and a lot you can do to eliminate the problem.
METAL CLAY BUBBLES
Metal Clay is a porous material, and the way pieces are constructed can cause issues. Bubbles may form from air coming through the porosity of the material or from an area where joins were not sealed properly. This type of bubble will usually be large and obvious.
Porosity can be dealt with by ensuring proper burnishing after firing. Tumble for at least 2 hours. For smooth areas, use ball tip burnishers to really compact the surface, closing off the pores.
If you are stacking pieces to create your piece, make sure the top and bottom are well sealed together with paste before firing. Gaps can cause bubbles.
ENAMEL BUBBLES
Most bubbles come from the enamel itself and how it's applied. These types of bubbles tend to be very small and are the real culprit when your enamels don't come out looking clear and deep. Tiny bubbles, even the microscopic ones you can't see, refract light. That means instead of the light penetrating all the way into your piece, it gets bounced back out. This will cause the enamel to appear hazy and obscure the underlying metal.
Fines: Fines consist of the super fine dust in the enamel that is created during the grinding process. This dust traps a lot of air in your enamel and will certainly make it look cloudy. Removing the fines is your first line of defense. They can either be washed out with distilled water or screened out.
Sizing: When you buy enamel, it comes 80-mesh. That means the ground enamel was passed through a screen with 80 holes per linear inch. You get everything that passes through the screen, from the large 80 mesh particles to the fines. You can improve clarity by sizing the enamel so you have smaller, tightly packed particles. I use 150-mesh and 325-mesh screens. Instructions for this are in my screening video at the 4:23 time mark.
Application: When using wet application, It's important to apply enamels in thin layers. If you pile a lot of enamel into a space, air pockets can get trapped in the enamel and cause bubbles. Applying and firing in thin layers helps alleviate this problem.
Surface tension: The surface tension of the water can cause issues as well, trapping bubbles within the water you use for application and making it difficult to get the enamel to lay down flat. Up until recently there wasn't much to be done about this. Now I have a new product out called ClearNamel(tm). It's a wetting agent that reduced the surface tension of water. This allows you to apply the enamel much more easily and eliminates most of the bubbles in the water used for application. The difference in enamel clarity when you use ClearNamel(tm) is striking! You'll really see all the way to the metal with none of the bubble refraction you usually get.
Here's a video on how to use ClearNamel(tm)