Glaze Trailing, White Over Black

In my last two firings, one soda, one stoneware, I've been experimenting with glaze-into-glaze trailing (as opposed to glaze-onto raw clay, which is also fun.) Specicifally I am interested in a white-on-black look. I've had two successes, each using This glaze as the black base:

Satin Matt Black

6500 Alberta Slip
1500 Neph Sy
1000 Strontium Carb
1000 Talc
Colorants:
1% Chrome
2% Red Iron Ox.
2% Manganese Diox

This began as the Cushing Satin Doll Black from the Watershed Glaze Book, with two substitutions: where the recipe calls for Albany Slip, I've substituted Alberta, one-for-one; and where to recipe calls for Barium Carbonate, I've substituted Strontium Carb, in a one-for-two ratio, i.e., half as much. (I don't keep barium on hand, for all the reasons.)

My first effort was trailing Coilles Clear (recipe below) over top. What I really expected was a shiny-over-matte effect, but all black. Surprisingly, the Coilles turns a cool white. I enjoyed that effect, so I tried an actual white glaze (recipe below.) This was a very clean, graphic, white-on-black effect. I was surprised how well each glaze held its shape, even on verticals, but so far I have only done small dots. Possibly these heavier lines will be more affected by gravity in the kiln, and therefore more distorted. I am open to the possibility that a distorted pattern, especially if it is unevenly distorted, may be better still!

Coilles Clear (from the Watershed Glaze Book)
500 EPK
7900 Cornwall Stone
700 Zinc Ox
900 Whiting

Waxy White (not sure the origin, but I got it at Portland Pottery)

4100 Custer Spar
1200 Gerstley Borate
700 Dolomite
1500 Talc
500 EPK
2000 Silica