You could be firing too high, or too long-

Are you firing at 1450?

Hi Brendan,

According to Thompsons Notebook on Transparent Clears - 

"Fire at 1450-1550 F for 3 - 5 minutes or until all copper oxide is dissolved -

2007 - a soft fusing clear that easily absorbs copper oxide.

2008- A low expansion clear used as the base coat for the crackle technique when Liquid Form-water base enamels are used for the second coat. 2008 is also good as a cover coat when working on titanium white steel panels.

2009- This soft fusing clear will clear up on copper on the first firing. It may produce "break up" or "pull through" when a subsequent coat of enamel is fired high.

2010 - This soft fusing clear will clear up on coper on the first firing but requires more time and /or temperature than 2009. It may produce "break up" or "pull through" when a subsequent coat of enamel is fired high.

2015 - This medium fusing clear has a gold color similar to Thompson lead bearing 1005 or 426. It works well under warm colors.

2020 - This clear does not "yellow" on silver. It should always be used when a clear enamel is needed on silver as the first coat. It may also be used on copper and gold. It is also the clear transparent that is suggested to be used as a final cover coat in that it has a lower expansion than  most of the other transparent colors.

2030- This clear is the best all- purpose -use clear. It works well under other enamels, opaques and transparents. Fire sufficiently to dissolve all copper oxide (reddish brown color). One or two refirings may be required.

2040 - This clear is harder than the above transparent clears. It is least likely to develop "pull through" when applying subsequent applications of enamel It should be fired sufficiently to dissolve all copper oxide.

With that said - Fine Silver or depletion silver does not have the high content of  copper oxides that copper has, and does not need to be fire so long and so high.  Also make sure that the enamel colors you are using are the appropriate softening pt. number when layering colors.

2010 has a low softening point of 842 F -  

#2020 has a medium softening pt. of 905 -  

#2030- a medium softening pt of 878 F  

 2040 a hard softening point of 914 F.  

You might want to use 2010 as your last clear flux layer as it's softening number is the lowest.  Don't overfire.

Hope this helps!

Have you looked on Thompsons web page? They have many articles on enameling and techniques. The key to enameling is knowing which one of your enamels is Hard, medium, and soft melting - and layering them appropriately - The hard enamels which take longer to come to a melting point should always be on the bottom and your quicker melting points (soft to Medium) should be on top - Sometimes enamel pieces go into the kiln for many firings, depending on what you are doing - so you want the bottom enamels to withstand the heat without burning out as you add more to the top layer. Same with the flux - 

Your foundation is important and so is making sure you have a good coverage on the back counter enamel - as the metal expands and contracts in between both layers of enamel as it heats and cools - Think of an oreo cookie - 

Good luck!

Trish