Travis,
1400 is WAY too hot for FCG!! Most manufactures suggest the burnout temp to be around 850 F. But we've found that to usually be just a bit too low. So we typically set our oven at 950. But if you're using a 77% AU then I'd even consider setting it at 900 F.
The problem with casting gold into too hot of a ring is that due to the golds low melting temperature, if it's thrown into a HOT ring, the gold stays in a molten state for too long of a period, and the heat of the metal, itself, can cause an internal boiling effect. If the porosity you're experiencing runs deep and at different levels, i.e. you discover more and more as you polish back, then this is most likely your culprit. Try setting the burnout temp lower and let us know your results.
Brian
I have to disagree.
Most metal manufactors have two burn out temp recomendations. One for Low Heat investments which is between 900 to 1000. The other for High Heat investment which is between 1200 to 1400.
If you are using a High Heat investment but only taking it to 1000 it is black because you are not burning out all the gasses.
Casting temps of most FGC alloys is around 1800, putting that into a 1400 ring is not to hot.
I use CB 30 investment. I burn out at 1600 for 1 hr. Crack the door half way till the temp drops to 1450. Close the door and give it 10 minutes then sling the metal. It adds about 15 minutes to the burnout process.
Ive been doing this for about 15 yrs. I get consistant fits and no porosity.
Assuming that you are not overheating your metal your problem is more then likely an undersized reservoir on your sprues.
I found that the preformed sprues do not have a large enough reservoir for many of the crns I do weekly, and I ALWAYS get porosity on these crns where the sprue is connected, and if they are really large it is over the entire crown.
What I do for about half my FGCs is make my own. I sprue it with a short 10 ga sprue, then I take rope wax and roll a ball/reservoir about the same size of the crn than attach that, then add a short 8 ga sprue on the reservoir to attach to the sprue former.
It takes me about 30 seconds to sprue this way, but its alot quicker than remaking the crn because of porosity.
It also makes a large button.
Ill bet a steak dinner that Im right.
Al