I don't think I totally have my mind wrapped around the whole hypo mess either, but I'll try to explain. If I screw up somewhere, hopefully someone will correct me.
Lavas are a totally different type of hypo than the one most people are familiar with.
As far as I know, there are 4 different types of hypos and they are all incompatable with each other (in other words, if you mated one hypo with another type hypo, all the babies would be normals het for both hypo genes).
The different types of hypos:
Hypo A
Hypo B (also called Sunkissed)
Ultra hypo
Lava
So, you asked how to make a Lava with a Hypo...you can't. To get a Lava, you have to find someone with Lavas and get one from him. Joe Pierce (Snakes Alive) is the main person selling these at this time.
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alstiver@hotmail.com
1.0 2001 Hypo snow cornsnake
0.1 2002 Pastel Ghost cornsnake
1.1 2002 Bloodred cornsnakes
0.1 1998 Het Hypo, Het Caramel cornsnake
1.0 2000 Hypo Het Caramel cornsnake