Andrew Birkett's nobugs.org
Ah, a little problem!
The two parts of the mould came apart fairly cleanly. I don’t think the corn flour worked very well at all. With hindsight I can see that corn flour will turn into a sticky gloop, unlike talcum powder or Proper parting dust. Also, the wooden pattern was quite rough, and the sand stuck to it slightly. Forgetting to cover the bottom of the pattern with parting dust didn’t help either!
To remove the wooden pattern, I put a screw into the top, gently tapped it with the sprue-rod, and carefully lifted up. You can see what the mould looks like now that the pattern has been removed.
Hmm, it’s not great. Some of the sand has broken away as the pattern came out. But it’s still got potential. I carefully used my fingers to push the bits of sand back into place. After dipping my fingers in water, I smoothed the sand back into shape. By pressing down on the sand, I could “rejoin” it back together.
I used an old kitchen knife to cut a channel from the bottom of the sprue pin to the cavity, and rebuilt up the edges with my fingers.