Back to Ganoksin | FAQ | Contact

First white gold casting


#1

Did my first 14kt white gold casting yesterday and had some
questions for the pros that will help other newbies as well as
myself.

I’m using perforated flask 2.5 inch by 4 inch in a VIC 12 and
electro melt furnace. I placed the flask in the well, hit the switch
and took maybe two seconds to hit 25 pounds on the pressure gauge and
I poured.

Normally I do 14kt and Argentium at 1,810F for pouring the metal and
1,050F for the flask that has cooled to that at least an hour. That
works fine as a general rule, increasing a little or decreasing a
little for heavy or fine pieces.

For the white gold I used a pour temperature of 1,945F and 1,125F
for the flask. When I poured the metal seemed to gob up into a big
round blob and left two round blobs in the crucible. I chalked it off
to a bad try and thought I should increase the pour temp by 50
degrees. I let it cool 17 minutes and grabbed the spaghetti colander
to catch the glob after plunging.

(the wife was not home so she would not know!) To my surprise the
casting came out. It was a single wedding ring, size 8 and about 8
grams. The metal did not pool and swim like I am accustomed so I
expected a failed cast. I had a few surface pits that have almost
polished out. Not sure what caused those.

So, should the metal be hotter? Should the flask be hotter? Should
the button be flat on the top as it is with the 14kt and silver? The
metal was Rio’s 14kt white from Canada and is polishing at a very
bright white. They recommend a pour temp of 1,886F but I know there
is a variance in the furnaces. I didn’t want to try 100 degrees over
on my first shot.

I’ll be trying rose gold next.

Thank you for suggestions.
Charlie


#2

Re: 14K white from Rio Grande,

When casting with a closed system like the JZP, the metal temp can
be set within 20F degrees of the recommended cast temp of the metal.
This type of system controls the melt temp very accurately.

In an electro melt, the temp is measured differently. The set temp
also is also dependent on how much metal your melting and pouring.
Since the pool of metal is not measured from the inside of the
molten metal the temps usually need to be slightly higher. You may
need to be as much as 100F over the recommended cast temp. The metal
does have to be completely fluid before you pour.

If the metal was slightly thick, I might try increasing the temp by
another 25F and see if you a more fluid mix. Again this will depend
on the amountof metal your melting. Smaller loads are harder for an
electro melt to determine the metal temp.

Hope this helps.
Phillip Scott

Technical Support
Rio Grande
1.800.545.6566


#3

I had a very similar experience recently Charles. Was helping a
client cast wedding bands in Rio’s 14k white gold. I followed their
recommendations for casting temp using my electromelt, a non
perforated flask and vacuum casting machine. I poured and it was a
bit gloppy, not a flow. All poured out of the electromelt though. I
was sure I poured too soon, it was not hot enough and that I would
have a partially filled mold with the client standing right there.
But we waited the recommended time and quenched. Sure enough we had
a complete casting that looked very good. In clean up I found only a
minimal spotof porosity. Crazy. I had not worked with that alloy
before, preferring to avoid nickel whites in my work. The client had
purchased the alloy. Was sure glad it worked though. :slight_smile: Your pour
temp and flask temp sound higher than what I was advised. I do
understand going a bit higher to account for possible temp
differences of the furnace. I did not go higher. So it may just be
the nature of that alloy to not really flow. Casting temp advised to
me was 1886F, flask temp 900-950. Flask temp might vary though
depending on if you are doing very fine work or not, like little
filigree, as you know. Hope my sharedexperience helps. Cheers- Carrie
Nunes


#4

Charlie,

Glad cast came out.

I predominately do sand casting with 14K yellow, rose, green, and
white gold.

All look different.

Just a friendly WARNING - the wife will ALWAYS find out - re using
kitchen utensils for casting.

Mine says my nose twitches when confronted.

Jeffrey


#5

This doesn’t really address the original post but I thought I’d post
it in any case.

When I first learned how to cast (centrifugally) with an oxy/propane
torch the goal was to get a complete casting, fully filled. Wouldn’t
that be great?

With that hurdle met and as I began to cast more the goal shifted to
the quality of the casting. You all know what that means:

-no inclusion pits, such as flux or investment
-no hot tears or cracks
-no shrinkage (shrink spot) porosity.
-no brittleness
-ductile, workable metal.

Casting is one of those things that is a sum of its variables.
Trouble can begin in the wax, the spruing, the investing, the
burnout, the casting, the cooling and/or the finishing.

If the waxing, the spruing, the investing and burnout are all good
there’s still something big: temperature. Not only the metal melt. A
really big piece of the casting puzzle is the temp. of the flask when
it is pulled from the oven or kiln. In my experience this is keyed to
what is inside, how much volume of metal there is. Whether it’s a
fine, netlike wax or a heavy sterling signet.

My results greatly improved when I learned that a lot of trouble can
happen as the metal mass cools. The longer the cooling takes, the
more coarse the casting and the more brittle it will be. It’s a bit
counterintuitive (it was to me) in that a larger mold cavity is
easier to fill: it takes longer and the air can evacuate more
quickly. A finer casting fills more quickly and so can be harder to
fill due to the back pressure of the trapped air which must evacuate
more rapidly. Even though there is less air it is harder for it to
get out.

The metal is cooling as soon as the torch is pulled away so I pull a
flask containing a finer model from the kiln at a higher temp since
it will be more difficult to fill. Also, the mass of metal is much
less, so cooling will happen more quickly and the casting will be
finer “grained” --the crystals will be smaller. (Jim Binnion, please
correct me if my understanding or terminology is off).

Heavier mold chambers are comparatively easier to fill. The
compromise here is that less advantage is lost due to a cooler flask
(it will still fill) but much is gained by having the larger metal
mass cool quickly.

Proper spruing and things like chill vents can control shrinkage
porosity but mold temperature has always been super important in my
studio. If I were making multiples, I had the luxery to play with
flask temps, lowering them until there were incomplete castings and
then bumping back up again.

Obtaining a fine grained casting was even more important when I used
to cast crowns and bridges in a dental office. It’s been my casting
goal since then.

A