Bronze Clay Success!

I have been fooling around with my special blend of home made bronze metal clay for awhile and have made some beautiful things but have gotten inconsistent results.  Then I moved up to a Paragon Max 119 kiln so I could fire cone 6 pottery as well as glass and metal clay.  I also started trying to make hollow forms in the bronze clay.  I was having problems with under firing and over firing, so I needed to tweak my firing schedule.  I found this article by Mardel Rein to be invaluable.Top Shelf before firing All sintered

Here’s a pan of unfired bronze clay before kiln firing.  I prefer to fire in these heavy, shallow stainless steel pans I get from my local Asian supermarket.  I find that the more you use them, the less they flake.

The ring on the right is perfectly sintered and not overfired.  The one on the left, from an earlier firing, is over fired.Hollow forms

Here are a couple of hollow beads.  The one on the left has been repaired.  The one on the right has not.  I have found that you must put hollow forms through two firings.  The form will come out of the first firing looking sintered, but will break if you drop it or hit it with a hammer.  I save up beads that have made it through one firing and put them through the next firing with whatever else I have.  I don’t plug the holes and I don’t construct screen cages to fire them in.  I just cover them with carbon and whoop-de-do.  You can’t use cork clay to make hollow beads from bronze clay, because you will never be able to get the cork fired out in an oxygen-free environment which is what you create when you fire in activated carbon.  But if you can construct a hollow form with holes and get it through two firings, you should be able to bounce it on concrete without it breaking.  In theory.

OverfiredLThe piece on the left has been over fired.  The pieces on the right went through a later firing and the tip of one broke off.  Rather than try to reattach it,  I just sawed the other tip off and will design something around the new shapes.

Repaired pair

The piece on the left broke in the middle during an earlier firing and I repaired and refired it.  The piece on the right is made up of broken sintered and unsintered pieces from earlier firings for a kind of mosaic pendant.

These pieces went through one firing schedule and sintered perfectly.  What I learned from all my experiences is that when you have thicker pieces, the trick is not necessarily to fire hotter, but to ramp up to temperature more slowly.  I started out firing to 1550 and holding for two hours.  Then I tried two and one half.  Then I tried three.  Thin pieces  were over firing, but hollow beads were breaking.  Then I tried lowering the temperature to 1500.  A little better but same problem.    Then I read that a slow ramp worked best with bigger pieces.  I tried ramping at 250 degrees F to 1000F, holding one hour, then ramping on full to 1500F and holding for three hours.  That did the trick.  All the single layer pieces are coming out fine.  I take the hollow ones out and put them in the next kiln batch through the firing cycle a second time, and they have been fine so far.   You have to experiment to find out what will work for you.

 

 

Still on Hold

I wrote a few weeks ago about how my basement studio was in a state of upheaval due to the installation of New Gizmo in the back part of the basement.   Since New Gizmo replaced the  boiler and hot water heater,  does not use the chimney for ventilation,   I decided to move my kiln and polymer convection oven to the back basement and install a ventilation system using the chimney.  I already have a ventilation system in the front basement that I installed for soldering but which I found worked beautifully when I was cooking polymer and firing bronze clay.  Read more about that one here.

I still haven’t decided whether to install a downdraft vent for the kiln or to go with a hooded vent that I can use for the kiln and the convection oven.   I already made a plenum cup that fits into the kiln’s rolling stand  right under the kiln, but I have hesitated to drill the small hole in the bottom of the kiln that the downdraft vent would need to function.  If I made a downdraft vent for the kiln,  I would have to be able to detach it from the inline fan and connect separate ductwork to hood to ventilate while the convection oven is operating.      I think I am going to set up hooded vent first and see how it does before I make the final decision.

1inlinefan

Here’s the inline fan I ordered from Amazon.  It’s the same one I have in the front basement.  It’s not too loud, has a variable speed controller, and does not require any special wiring.   I will have to bolt it to a piece of wood to steady it.   I could bolt it from the ceiling, too.    I will need two 4″ to 6″ vent reducer/increasers to connect each side of the fan to the ductwork.  I also ordered them from Amazon.   One will connect to ductwork that hooks into the  4″ chimney opening behind the fan and the other one will connect on the other side of the fan to a longer section of ductwork and the vent hood.

My electrician installed an extra outlet  for the fan and the convection oven.   The Paragon Max 119 kiln runs on 120 volts but does require some additional wiring and a special outlet which Stubewan the electrician also installed.   He also left me some metal tape and ductwork to use.  Thanks, Stu!

I used a wok lid for the vent hood in the front basement.  I will use a stainless steel mixing bowl for the vent hood in the rear basement.

BowlHood
Bought at a house sale for $5.00.  I will saw out a hole in the top and  attach the ductwork.

At this point, I plan to attach the ductwork and hood to the wood beams in my basement ceiling and raise and lower the hood with a chain.

 

 

I plan to stow the kiln under the stairs and move it out to the middle of the floor for firing.   I was hoping to get it all hooked up this week, but Amazon sent the wrong size reducers.  Back they go and new ones ordered.

Wish me luck!