Hi Orchid, First let me apologize for the possible lack of spaces
between some words. I’m not are why but this happens in my posts to
Orchid, maybe it’s yahoo mail? As I’ve written before I’ve
experienced problems intermittently with extreme brittleness in my
argentium castings. I thought I’d solved the problem but it has
returned with a vengeance. The last few times I’ve casted about half
of my castings have come out so brittle they break with even just
the slightest bit of bending. It seems likethey’re full of
micro-cracks that require only a little bit of stress to reveal
themselves. I thought before that it was an issue with incomplete
burnout due to lack of oxygen, so I added a vent hole in the door of
my neycraft kiln and have started to crack the door of the kiln open
for a few minutes at the point where the wax fumes begin to ignite
around 950-1000 degreesF. This results in some flames exiting the
top vent, something I assumed meant there was adequate oxygen for
combustion.
I use a high ratio of of new metal to old and make sure to clean the
old metal very meticulously before adding it to the melt. I melt
with an electro-melt furnace using a small amount of casting flux.
All the variables I can think of have been considered. This evening
I poured two flasks of filigree earrings, the flasks are 3x5, burned
out for about 9 hours. the melt temp was 1830 F and the flask temp
was 1025. The flasks appeared to be fully burned out, with white
investment and no discoloration around the sprue hole. The castings
from the first flask came out grey-black in color and extremely
brittle, with yellowish investment surrounding the castings. The
second one was farther from the door and came out slightly better,
though still a bit grey-black towards the button and more white at
the top. Castings that come out white in color are fine while those
that are more grey-black, sometimesmottled tend to be the problem
ones. The black color seems to seems to indicate incomplete burnout,
but when I remove the flasks from the kiln to cast they seem to be
fully burned out. Is it possible that I am overheating the
investment causing it to break down and release sulfur? I make sure
not to get it over 1350 F but perhaps my thermocouple is incorrect?
Also I’ve noticed the investmentaround walls of the flask
occasionally has a bit of rust color, presumablyfrom the flask,
though I do clean them before investing. I am just about at my wits
end here, If anyone has any ideas about what may be the cause of
this problem I would really appreciate hearing them. I’ve been
casting for more than ten years and its quite frustrating to be
unable to diagnose this issue. Thanks. D.