MY REPLY: Looking at your images I wanted to first say that not everything is silver stain. Forgive me if you already know this but only the ornamentation in the diamond quarries is silver stain. The yellow brown tone that appears to be fading off is some other pigment. I have attached a photo with some arrows below.
|Not everything is stain.|
Silver stain is very permanent as it is absorbed into the glass itself and not subject to corrosion from atmospheric weathering like vitreous pigments are.
As to the silver stain, I made many tests as I was preparing my book on stains. Here is a photo of my test on Lamberts glass:
|My tests on Lamberts Glass|
I think you will have the best results with Reusche 1383 or Keracolor using a mixture of 1 part 76050 to 4 parts 73028/A. You will need to experiment to get the density of the application correct. Prepare two identical samples with a heavy to thin gradation application on Lamberts glass. Fire one sample and then you can compare the results to the unfired stain. Stains look radically different after they are fired so a fired/unfired sample is extremely beneficial. You can mix the stain with any medium but using oil may allow you to make a more controlled gradation. Silver stain is best fired between 538C/1000F - 593C/1100F Try this schedule as a starting point:
90 min to 540C/1004F
10 min to 580C/1076F
Hold for 45 min
If the stain is too heavy after firing it can be lightened with a cotton swab dipped in hydrofluoric acid - use extreme caution when working with acid in this way.
If you plan to fire the stain several times - make a test for this as well - stains can intensify during successive firings. I had a stain appear to "not take" once I washed off the clay body (all stains are premixed with ochre/clay). I refired the piece - without reapplying stain and it came out beautifully. Even knowing as much as I do - stains can remain a mystery :)! My best advice is to test, test, test and keep a good log - be scientific in your approach.