Sue Reilly (Mrs) at the School of Marine Biology and Aqua Culture and School 
of Tropical Biology at James Cook University in Townsville, Queensland, 
Australia has a problem with agar. She doesn't specify exactly what her agar 
is.

Agar (a gelatinous material from an east Asian seawead) has been used as an 
embedding medium for a long time. I've used it in surgical pathology, but it 
slows down grossing so much that most laboratories don't find it practical, 
particularly because (by long inexorable tradition) we don't have dissecting 
microscopes.

The books usually suggest a 3% (presumably w/v) solution in water. I've 
commonly borrowed tryticase soy agar from the microbiology laboratory. It's 
convenient to have a blood bank heating block to keep it melted.

In the last few years a commercial product called Histogel has come along, 
more convenient to handle than preparing your own agar. I suppose it's 
available in Australia.

Finally, since you're Down Under, your problem may result from embedding your 
specimens upside down!
;-)

Bob Richmond
Samurai Pathologist 
Knoxville, Tennessee