http://abrahamlincolnartgallery.com/...fsculpture.htm
This quote is from the site above, I found the essay on 'Subtractive vs Additive' sculpture interesting.
'Michelangelo, created his works first in clay. Â*The clay would next be cast in plaster and a three dimensional [glow=red,2,300]pointing device[/glow] would be used by a staff of assistants to transfer the dimensions to a block of marble'