Hello from Sunny SF,
I have casted for many years & we, too, have done a lot of organic
materials. This would include twigs, peanut shells, pistachio
shells, poppcorn, ferns, eucalyptus pods,& orchids…We always make
sure that these are sprued well, sealed with some kind of
sealant(paraffin wax, furniture polish, varethane etc.). It has
never occurred to me that weighing would be that much different than
calculating for waxes. Of course, we have always done more that a
few and we based the appropriate amount based on this:
Pre-weigh base and add all pieces/sprue up. Then weigh finished base
minus blank base (tare) to get weight of all pieces. Then multiply
by 10.46 to get casting weight in silver…BUT don’t forget to add
extra forthe button…So, for example on a 2.5" X 2.5" flask:
Filled base is: 2 dwts.
X 10.46 ( specific gravity for silver)= 20.92
Plus button–I would allow about 15-20 dwts extra…
Thus total could be 35.92/36 dwts to 40.92/41 dwts…
I’d probably cast at 41 dwts…This assumes a cone button for a
2.5 flank & fitted base.
So, I’m saying like the other metalsmiths/jewelers—Treat it like
wax, no real differences for calculating…Oh, by the way, when I
taught at CCA last year, we also did silk flowers-same way…A
student coated them with a sealant, built up wax thickness &
cast…And, we also did some insects, including dead bees & dragon
flies(no animals were killed to do these projects.
In other words, they were found expired) !!!
Ciao & good luck,
Jo-Ann Maggiora Donivan