I made up a few different slips from my porcelain body (Standard 130) plus 5% gerstley borate, and added varying amounts of Mason stains to them (1 to 2%) mostly blues and greens.
This was sprayed onto test tiles using a mouth atomizer, in bands without distinct borders. I was hoping for subtle gradations in color, but after bisque these tiles were pretty pale. I glazed them with various glazes I had on hand, and I got the most interesting result from a glaze modified from one of the recipes in John Britt's midrange book. This was a glaze with modest amounts of lithia and titania.
Since I've been limited to oxidation firing, I've learned to love titania.
Here's the test:
Click the thumbnail to see a better image.
The slips developed much more color after hard firing (Cone 8). The unglazed surface is like a very dry matte, but it did not stick to the shelves at all. I may try the next round with more boron, and I'd better put some food coloring in the slip so I can see where it goes when I spray it on. Presently the stains do not tint it adequately when wet.
You can see the unglazed slip at the bottom of the tile.
Do you mind sharing the percentages of titanium and boron you think started to arrive at what you were shooting for