Here's what happened; sorry for no pics...you'll have to trust me on this one!
All of these pieces were bisque - the glaze and decal applied for a single firing.
1. Top Left Purple: Decal OVER low fire clear matte glaze - black images (this is important) fired to 06.
Result - 5 stars! The image came out great - the black creates a perfectly clear iron ox sepia toned image. This is over unfired glaze. So, you can't move it around a lot - basically you get it on there and that's that.
2. Right Middle: Decal OVER low fire matte white glaze - fired to 06 - black image.
Result: 5 STARS! Great result over the glaze - which also means you may be able to eliminate a firing - uh, yay!
3. Bottom Left: Decal OVER low fire clear glaze - fired to 06. This image was a little washed out; the glaze pulled out a lot of the detail but it did not disappear; just a faded image. Again, sorry, no pics; I'll have to take them this weekend.
*also note that I put a grey toned decal image (you can see the compass) and it all but disappeared in the firing. So, black is the new black! Stick with black images to get a clear result.
All of these pieces were previously glaze fired to 06. We applied the decals and then low-fired to 08 on a fast fire schedule: again good results on all these pieces - barring the grey images; they were ghosts of their former selves. The black images worked perfectly.
All of these are low fire glazes; the top left a clear low fire glaze - the blue vase is underglaze with clear glaze over it and the red a low fire glaze.
I will say that the decal image on the red piece was a little faint - but strong enough. On the blue vase it looked almost orange!
The decals were from computer images and printed on decal paper.
If anyone has any suggestions or has experience - I would LOVE to hear from you. Please comment. This process is not full proof - I've talked with other folks and there seems to be a wide variety of results - I wouldn't run off and put decals on a piece you love - we have just begun the testing process - I will continue to report experiences with this process.