Decorating fired wares

I had been working under the assumption that transfer printing was done onto bisque fired wares.  There are good reasons for this not to have been the case for calico buttons.  The buttons themselves might have been produced at one location, then transported to another location for printing; my bisqued tests are too fragile to invite being dumped into bags and loaded onto horse carts.  If the same button was sold both in both plain and decorated forms, it makes especially good sense for the decoration to have been applied to fully fired wares.

My experiments with decorating fully fired wares had been dismal failures.  Ink adhesion is very poor; most of the ink comes off with the tissue.

Recently located, however, is a book by C.F. Binns: The Story of the Potter  published in 1901.  Beginning on page 217 (the book is readily available in scanned copies online), Binns gives a popularized but detailed account of the transfer printing process as used for household pottery.

Binns on transfer printing 

He notes that "a fine varnish" was applied to the wares to promote adhesion of the ink.  Taking that hint, I took a few fully fired test coupons from early body experiments, heated them, and applied a thin coating of #8 burnt plate oil.  The results are somewhat promising.  I have been able to obtain better ink adhesion, but I have increased difficulty in removing the tissue.

Another reference (specifics not remembered) suggests that a potassium soap was used in the process.  Binns states that the transfer paper is prepared with a soap and water solution before the impression is made.  Potassium soap stands to reason here, because potassium soaps tend to be liquids, whereas sodium soaps tend to be solids.

A readily available potassium liquid soap is Dr. Bronner's.  I am trying the Baby Mild (no fragrance) type; most of the fragrances contain terpenes that seem likely to act as solvents for the oil medium.  (I use one of the household citrus-based cleaners to clean ink off plates, hands, and utensils.)

I need to experiment with soap concentration to see if there might be one that allows the ink to adhere well enough to the tissue while making the impression, yet promotes release of the tissue from the ink/varnish/body when soaked after transfer.

Also, I have a few other types of tissue paper on order.  Some are sold for conservation and book repair, and claim to have good wet strength.  Thinking a bit about wet strength, I tried printing on tea bag paper: ink transfer was disappointing to the point of being useless, possibly due to porosity, though the wet strength was much better than for sewing pattern tissue.