Dyeing yarn

Last year I agreed to lead a workshop for my guild on how to dye a wool yarn to produce a striped yarn for socks etc. The date was end of June 08 which seemed like a really long way off at the time!
It finally crept up on me and I got everything ready - dyes, clingfilm, brushes, vinegar, yarn, table and so on. I asked the other members to bring their own yarn in long skeins (at least 9ft long) and clingfilm too.
I started by demonstrating, putting the skein round the table with a length of it on a piece of clingfilm. I painted each part of the skein with a different colour of dye, wrapping that length in clingfilm as I finished it. I left a few gaps between the colours so that when I came to knit the yarn it would have a few stitches in white every now and again. I followed the directions in the book I was using and so I used a ziplock bag with some water in it, instead of the big bowl I usually use for dyeing in the microwave.
I put the finished skein in the microwave for 2 minutes, rest for 2 minutes, three times and then left the skein to cool down. Then the other members of the guild painted their own skeins.
When mine was cool I took it out of the clingfilm and held it up triumphantly only to find that it all fell apart. Oh no, it had burnt where the unpainted gaps were left even though I had put extra water in the bag.
We cooked each of the other skeins in the bowl instead of using ziplock bags and they all turned out fine. Everyone else was pleased with their results. I did paint another skein and that turned out okay, but I was really upset with myself for burning the first one!!