|
This method
of casting has
been done for more than 5000 years. The ancient Egyptians,
amongst others were adept at it. In those times, beeswax and
clay and charcoal fires were used. Still, the principle remains the same.
Okay, so first I carved a ring and then I sprued it up and
attached it to the rubber former. The wax I am using is a
new wax I am trying out for the first time. It is made by
Kate Wolf. It is supposed to represent the gold colour. It
carves nicely, but the colour does not show detail up as
nicely as purple wax, which I normally use. The black rubber
former at the bottom has a convex shape in it which will make a concave
form in the plaster for the molten metal later. The wax is
weighed before it is mounted in the former ( also known as a
sprue base) and the amount of silver, in this case, can be
worked out. Silver is 10.4 times the weight of the wax ,14ct
gold is 13.4 times and 18ct gold is 17 times the weight.
Also, 20% extra should be added each time to accommodate the
button of the main sprue. However, in the case of poor
struggling artists with not enough money to afford extra
gold I have quite successfully cast without the 20%.
Here the ring is in the flask the flask is in the rubber
former.
Then I put a copper surround around the flask with masking
tape. This is to stop the investment (Plaster) from bubbling
over the top of the flask when it is vacuumed. I use copper
because it is easy, but plastic, vinyl are also suitable.
This is the powder I use. I buy it in 100lb boxes, but it is
available in 5lb quantities.
I measure the plaster out accurately and at the same time I weigh out
the water as well. This is normally mixed in a ratio of 40%,
but I prefer 38%. The temperature of the water will
determine how quickly the plaster sets. Some of my friends make
their water ice cold, then mix the plaster very thick,
saying it gives a better density and thus a smoother
casting, but I couldn't be bothered with that. I just do it
at room temperature.
I use a cake mixer to mix. The glass of water is the
pre-weighed water. I am only mixing 300grams of powder.
Straight after mixing, the plaster is poured into the flask.
It should be the consistency of thick cream.
Straight after pouring, the investment is vacuumed. Vacuuming
is the best way, but the wax model can be coated with a debubbleizer, ( dishwashing liquid is also ok)
then allowed to dry and the
investment is then vibrated as soon as it is poured in the
flask, which works so so. Some bubbles
will remain. These bubbles will then be cast and if the are
attached in a critical part of the piece, can be a real pain
to remove. I just vacuum the piece for about 90 seconds. In
the picture, I am using the vacuum side of a vacuum casting
machine. I don't like vacuum casting, but others do.
Once the plaster has set the
rubber former is pulled off. You can see the indentation in
the plaster that will collect the molten metal. The blue is
the sprue wax. This will be burnt out in the burn-out oven
Then the flask is put in the oven. Normally I would have
several flasks but in this case I want to cast in 3 hours
time. The oven is heated up slowly. First at 200C until the
wax is melted out and the flask is dry. About 1 hour. Then
to 500C for half an hour, then 700C for an hour then back to
500C for half an hour. That is the temperature I like
casting at, generally. With many flasks, this time increases
to up to 12 hours. It all depends on how many flasks there
are. The flask has to be white in colour when it is ready to
be cast . This means that all the wax has been burnt out and
any carbon residue left from the wax has been turned
into carbon-di-oxide, which is the purpose of this oven.
This is a basic 'broken arm'
spin casting machine. It is wound up with a spring. This is
a cheepo model, but it works just fine for me. I just
built the box out of wood and it has never given me trouble.
I can cast articles up to 500 grams with it. See the eagles
foot in
http://www.meevis.com/jewelry-making-class-experimental-casting.htm
In the picture I am heating the metal up.
Then the crucible is slid up
to the flask and the metal is 'super heated'. This is about
100C above it's flow point. This is to allow the metal to
remain in a molten state as it enters the mold. The metal
enters the mould under tremendous force, sometimes up to 50
times the force of gravity. It depends on how strongly the
arm is wound up. I choose the middle road. No need to kill
something by excessive force.
Action! Note the splash of
metal in the bottom of the box. This is because 'ol bright
eyes here forgot to weigh the ring before I invested it. So
I put in more that I needed, which is much preferable to to
little, believe me. And since I am casting silver, not so
expensive....
Once the machine has stopped
spinning and the button is not red anymore in normal light,
the flask is dumped in a bucket of water. This causes the
investment to disintegrate and the (hopefully) complete
piece is removed.
Like this . This ring was cast
because it is difficult to make by any other method. Not
impossible, but difficult. I always keep in mind that when I
work in a medium. I stay true to that medium. What I mean is
this. There is no point to cast plain wedding bands. They
can be made far easier by other methods. By the same token,
this ring is far easier to make in wax than fabrication or
forging. This ring will be smoothed and thinned out and the
a mould will be made of it. The resultant models will be
made to accept different tops with different stones set in
those tops.
This is the basic methodology
of spin casting. There are many variations of this method.
Other attempts can be found on my blog
http://hansmeevis.blogspot.com/2007/12/more-stained-glass-casting.html
These tutorials cover subjects relating to casting:
How to wax carve a cameo / image
Description of how to
tackle casting of insects in metal
Experimental Casting
Making a
mould out of the above Panel Ring
If you have any questions or wish to be notified of any new tutorials that are posted,
email me at hansmeevis.tutorials@gmail.com |
