Hi everyone.
I have been having terrible problems vacuum casting silver. Melting with an electric melting furnace and graphite crucibles
It seems to be impossible to vacuum cast silver without some form of tiny gas porosity. This porosity only shows itself after polishing and ultrasonic cleaning the rings as dozens and dozens of tiny pits.

I have some very basic casting questions which hopefully experienced people my know.

1. Does it matter how you pour the melted metal ? For instance a slow steady pour or tip it in as fast as possible.

2. Should I leave the casting machine vacuum pressure on after the pour whilst the can and molten metal cool slightly, or turn of the vacuum immediately after pouring the metal into the can.

3. Do graphite crucibles oxidize after only a few uses ( 3 to 5 ) and therefore the crucible may cause contamination of the melting silver.

4. Should I use borax in the graphite crucible.

5. I melt and then cast at between 1020 and 1040 celsius. Anything outside this range causes worse porosity.

6. I remove the can from the kiln after 8 hours and the temperature I remove the can is 550 celsius although with a laser thermoter pointed inside the can the temperature would then be 400 approx.

7. I allow 15mins to cool before I quench the can.

8. I have been using almost always brand new grain so old scrap is not a factor in my process.

9. I am using standard injection wax patterns, 3d printed wax is not a factor.

If anyone can see any problems here which im missing or can answer some of the basic questions I would be delighted with any help.

Best Wishes