I have also had a lot of trouble with shivering. I find that peach and
pink are the worst. I've used Velvet underglaze (Amaco?? and also Mayco
UG. I use low fire white from Laguna clay in Los Angeles. I really
like the Amaco sets that are dry watercolors, but the kids never prefer
them. They don't want washy colors but they always like pieces that
I've done using them. I've never had any shivering problems with them.
Perhaps the UG is too thick? Has anyone used the Concept glazes--I
think they are underglazes but also can go over glazes??? Sid