Question About Firing Up-side-down

[Scope Builder]

I am going to make some coasters for a friend and the picture below is the blank with the pattern cut and tacked (glued) to it.     I plan to fire this then cap it with clear in a second firing.  I want the lines to stay as crisp as possible.  My question is, should I do the first firing up-side-down?  Helpful advice will be greatly appreciated!!

[Becki]

I've never done this with less than 2 full layers but I imagine it could work with a conservative ramp up.

[Kev]

You might be wise to tack the pattern to a clear base with the white base behind it and fire it pattern side down. Once fused, flip and fire polish to get a smooth topside.

[Scope Builder]

Becki, a conservative ramp up is no problem and maybe a extra long bubble squeeze too.  Kev don't you think that if I fire all at once like your suggestion that I increase the chance of bubbles being trapped in and around the interior of the pattern?

Thanks for the ideas!

[Kev]

I'm with Becki in thinking that a 2 layer base  is a better way to go than fusing initially with a one layer base.

I'm thinking a slow ramp up with a bubble squeeze would eliminate most of the bubbles, and if you put clear on the back instead of next to the pattern, most of the bubbles will only be seen on the backside of the coaster. Fusing it all at once with the pattern down, followed by the white and then the clear should result in a crisp design with few bubbles . Then all you would have to do is a fire polish the top side to get it smooth again.

[Scope Builder]

Thanks Kev, I may try the two layer and the pattern down.  I may also fire one set face up to see the difference.  Thanks again!

[Stephen Richard]

If you were to decide to use only one layer above the upside down design, you need to make the blank larger than the final, so you can cut the dog boned shape down to the size you need. And you need to keep the top temperature down to no more than fire polishing.  But, yes it is better to do the proper thickness from the beginning.  This was christened "flip 'n fire" by Brian Blanthorne in Wales some years ago.  He has a very odd way of spelling things too.

[Scope Builder]

I decided to fire it with two white blanks with the pattern side down then today I flipped it and fired to fire polish.  I had to take it to 1425 to get the surface I wanted and actually it could have used a ten minute soak at 1425 but I didn't because I was concerned about devtrification.

The sides are much straighter than this picture shows, they are more like the bottom edge on all sides.  The color is also better than the picture.

[Stephen Richard]

Note that devitrification occurs in the region of 700 - 760C.  See the Bullseye Glass note on heat and glass
http://www.bullseyeglass.com/pdf/technotes_tipsheets/TechNotes_04.pdf
The devit can occur by going slowly upwards as well as downwards.

[Kev]

Looks like it turned out well. Good job!

[Joe]

Looks great, good work!