Is there any special considerations when casting with acetylene?
I cast alot of 18kpd white gold and have been advised that my
acetylene is not the best gas for this metal, hence the switch.
I assume you meant are there considerations when casting with
hydrogen... If you're using nickel white golds, be sure your flame is
not too too soft and reducing. Too much free hydrogen can lead to
the nickle absorbing hydrogen (just like fine silver absorbs oxygen).
It then comes out of solution on cooling, resulting in problematic
porosity. Hydrogen is great for casting or working platinum, but at
least in my opinion, perhaps not the best for casting golds, at least
those with nickle or substantial copper (which also absorbs/dissolves
hydrogen when molten) in the alloys. I prefer casting with either
natural gas or propane as fuels. Also as far as setting the flame,
you might check out installing a vapor fluxing unit on the gas
supply. These are standard additions to the "water torches", and
amount to some method of bubbling the gas through a flux mix, which
can be, for example, acetone with boric acid, or other such. It not
only lowers the flame temp a bit, which is nice so you don't totally
burn the metal with that high temp, but it also makes it much more
visible. and it's then self fluxing too. Without that, setting a
neutral flame can be helped by dusting a bit of boric acid or borax
on the end of the torch tip, which causes a sodium flare in the
flame, also making it more visible. And there's also always the
sound of the flame. As with other fuels, the sound changes when it
gets oxidizing. Also, if the lights are dimmed enough, the flame
isn't really invisible. Just pale. You can, with dimmer lighting,
see the flame structure, at which point you set the flame
characteristics the same as with other fuels.
Hope that helps.