[deb tarry]

I just want to throw this out there as I don't know for sure if it applies to what you are doing.
Within the coe's there is different viscosities meaning even though they are considered to be compatible they seem to take more heat to melt and stiffen out of the flame faster than others. An example in soft glass would be ivory vrs black or clear. (anyone who has made the classic tiger bead has experienced some cracking issues especially if the base was the ivory and not black). Within the boro family you have the same thing, and if you throw in the metal from the key you have another expansion and contraction issue.
So if one color combo doesn't work try another also do some 'flame annealing' (I know you can't anneal in the flame) but what I mean by that is even out the temperature of the piece by going in and out of the flame keeping an eye on the color temperature. In the flame until it just starts to glow take it out of the flame until it disappears then back into the flame. For a small bead like what you would be making on the keys is approximately 5 seconds in the flame 5 seconds out doing this several times. What this does is evens out the inside temperature with the outside temperature before it is put into the kiln. Hope it works out for you cause those keys are cute.