toadslayer - i listened to an interview with the late beryl cook once. she did exactly as you do - she said she always put her "ladies" up in the loft for a while then could alter as nec when she got them out again.
She also said when she heard the official art school view that black paint was a no no it made her laugh because she uses loads of it. Being self taught no-one had been able to say "don't do" so she had the freedom to paint as she wanted - and certainly as many of her legions of admirers wanted!
If a tutor is negative go eslewhere - their job is to encourage and bring out the best in an individual - not to discourage, nor to convert the students painting style to what is "accepted" or to only show them how to work as the tutor works..I'm a great fan of self study - you learn by mistakes - and there's plenty...but no-one says don't do that. I like to see for real how a new material is used and the properties of it if possible - but with the amount of books, dvd's and art help forums online it can be done alone
the only reason i wish i'd gone to art shcool/uni is the materails - to get my hands on and in lots of different stuff that they have would be fabulous. Instead i have to wait for a sale and then buy more - and of course stuff like kilns etc simply isn't feasible

well not unless someone buys everything i have

and thats about as likely as my winning the lottery jackpot.
