I've read that you should mix fondant and tylose in order to get the correct consistency for pearl borders. If you're not making fondant from scratch, but are buying the fondant, how can you get the correct consistency?

It's pretty inexact.

I usually just sprinkle some on and knead it in. Once the fondant stretches a bit, but "breaks" (as opposed to pulling out a long way like chewing gum), I'm good to go.

If I need a substantial amount, for Satin Ice I knead in 1 tsp./lb. With Wilton, I knead in 1/2 tsp./lb because it's more firm to start with.

HTH
Rae