First Vacuum Castings

Investment is Pioneer Smoothcast from SRS, mixed at 100/38 as per instructions. I mix for 3 minutes, vacuum for 3, pour and vacuum till 12 minutes has elapsed, gloss off is around 17 minutes - probably slow due to low ambient temperature in my workshop.
Burnout is as follows:- as slow as possible to 270 C, hold for 3 hours, ramp to 730 over 2 hours and hold for 3 hours, drop to casting temp, guessing at 600 C and hold for 1 hour then cast. All temps are very approximate - see kiln picture on previous page for why.

Sterling silver cast of four vaguely Celtic emblems molded from customers original - requested a gold version so this was a test. Lots of little bumps on the casting where air bubbles were present in the investment but  they will clean off and the cast was complete - so 4 useable items, well impressed for a first attempt.
Silver was clean scrap, torch melted with oxy/acetylene and a little borax added as flux.
Emblem is approx 2cm or three quarter inch across.

Second cast is two of the same model in 9ct gold, still using clean scrap for the charge but no air bubbles this time since I vacuumed for longer and both pieces polished up fine.
Really impressed with the detail attainable - the hallmark from the silver original was still readable and had to be buffed out.
Finished item is 0.9g in 9ct gold and total cast was only just over 9g.

Next project is to cast this in 22ct gold (using sovereigns). The original is some sort of low melting point alloy and plated yellow, approx 2 inch square and one eighth inch thick - intended for a brooch.
I have a good mould and the wax weighs in at 1.95 g so at a density of 17.3 for 22ct Au I am looking at finished item of 34g.
Suggestions on the best way to sprue this item would be most welcome, the finish on the back is irrelevant so that helps a lot.