A King's Crown or Ruby Thumbprint
wine by Adams ca 1890


Welker defines as:  "A process of coating a piece of glass with a chemical whose true color is developed by heat.  The staining material is painted on the annealed [cooled] article with a brush wherever the decorative effect is desired. It is then fired on for permanency at which time the glass assumes the desired color."       


This fired-on coloring was added after the glass piece was made.