Day 34: Smelting
night I was worried about the crucible that we put the gold into. I was
told that it was a graphite crucible and I was worried that it might burn
along with the coals!! This morning we found out that I needn't
have worried. It was all still there.
Mike brought it out
and I had the honour of turning the crucible upside down and tapping out
the gold! What we had was a large lump of what looked like glass with
some gold specks hidden within. I took a hammer and broke the glass to
reveal the gold - very exciting. The gold looked great but unfortunately
it was not in one piece to work with. We really wanted an ingot to be
able to make something with but what we had was about 4 gold lumps. So
we agreed that we could fire up the furnace again to try and smelt the
blobs into one piece but that I would also think about another way of
tackling the problem now that we had got the pure gold from the smelting.
idea that had been buzzing around in my mind was to try and make a carbon
arc to melt the gold. This consists of connecting up a car battery to
two carbon rods. When the rods touch a very high temp spark is generated
between them up to 3000oC. The carbon does not melt or react
with the gold and so it might be possible to heat up the gold this way
and make a single blob.
I took a lantern battery
apart to get a source of the carbon rods. These were cleaned up and then
fixed onto copper tubes and then onto the car battery terminals. Striking
the rods together made a wonderful bright white light arc. It also burnt
away any of the impurities that were left in the rods. Then I put the
gold pieces into a crucible and started to arc to melt them together.
As the temp got higher the gold melted and through my welder's mask I
could see the gold flowing together it was all very exciting!
When it had cooled
and I had taken the mask off I was horrified - our wonderful gold that
we had worked so hard to make had turned black!! But I was soon relieved
as the black tarnish was only skin deep and it came off easily with a
The next step was
to try and use the little time remaining to make something. I had wanted
to make a Maori design and although jade is the usual material of their
choice thought that something along these lines might be appropriate.
I chose to make a sort of Maori fish hook as this was not only a lucky
symbol but seemed to be appropriate to me as it represents my Rough Science
efforts at making tools and machines. So I was filmed sketching out some
designs and then the rather anxious moment to start cutting, filing and
polishing the gold!
basic gold shape was easy to cut out as the gold is soft (it's almost
24 carat) but I had a great deal of trouble drilling it. It seems that
there must have been some tiny crystals of much harder material trapped
within the gold because every so often I would drill a hole and the drill
bit would brake off in the gold. This happened three times and in the
end all I wanted to do was to make a hole for a thread so I gave up and
used another technique. In the meantime I had wasted a lot of time and
caused a large fracture in the body of the design. It wasn't going
However I persevered
and ended up with something that looked quite nice although it looked
like a little shrimp more than a Maori fishing hook. I also used one of
the garnets I had found as an eye for the design that looked very nice.
The garnets added a sort of Celtic feel to the Maori design which was
appropriate, I think. Mike L thought the final thing looked like whitebait,
which is a speciality in this part of New Zealand, so maybe it was OK