Hi Samantha !!
Welcome to Art Glass Answers.
One of the big things we have to deal with, as glass artists, is the COE of the glass -AND- anything else introduced into the 'equation'. In this case, your mold becomes a component of the COE issue.
Stainless steel has a much higher COE than glass, usually in the 180 range. This means it expands about twice as much as say, Bullseye or Spectrum, -and more importantly- shrinks twice as much when the mold and glass cool.
In general, if the glass is OUTSIDE a stainless steel mold, everything will be OK. Think a piece of glass slumped OVER the bottom of a stainless cocktail shaker. By over the bottom, I mean the cocktail shaker upside down on the shelf. I think its pretty easy to visualize that as the glass and mold cool, that the mold will shrink *more* than the glass, causing the glass to release from the mold.
Any glass slumped INSIDE a stainless steel mold, will be a big problem, because as the whole mess cools down in the kiln, the stainless steel mold shrinks MORE than the glass, getting what I call a 'death grip' on the glass. If your mold is really, really shallow, then as it cools, the higher shrinking mold *may* push the glass up and release it. There is not a concrete, scientific answer as to what the shallow angle can be, because there are many factors that affect the ability of the glass to release from the mold, and the mold push it loose.
All that being said, I would ask you is this stainless steel mold *intended* to be a glass mold, or is it a *found object* that you'd like to use as a mold ?? If it is intended to be a mold by the manufacturer or seller of this mold, and you are using it as said manufacturer/seller suggests, then you might want to contact them. Additionally, I've had *much* better success using kiln wash on molds, instead of boron nitride. It's a lot cheaper too; I use the Bullseye pink shelf wash.
Why not post two pictures of the mold; one of just the mold, and the other with the glass on the mold. Also, is the glass cracking on the way up, temp-wise, or on the way down ??
PS - this looks OK, except it is overly conservative.
Rate 250 temp 600 Hold 10min
Rate 150 temp 960 Hold 10 min
Rate 300 temp 1290 Hold 10min
Rate 9999 temp960 hold 1.5hr
Rate 80 temp 800 hold 1 hr
Rate 150 temp 300
I would change the above to:
Rate 9999 to temp 800 hold 15 minutes
Rate 600 to 1290 hold as long as you need to get desired slump
Rate 9999 to temp 960 hold 45 minutes (I vent the kiln to try to do this in 10-15 minutes)
Rate 80 to temp 825, hold 5 minutes (I usually use 120DPH, ie 2 degrees per minute, but slower won't hurt)
Turn kiln off and let cool to room temp