No Pre-firing for White Bronze; One More Update to the Manual
Last week was dedicated to one of my New Year’s resolutions: improving the firing schedule of White Bronze. The result: White Bronze does not require pre-firing. Just fire in carbon at 1250°F/677°C (brick kiln); 1325°F/718°C (muffle kiln). Hold for 2:00 hours. Optional: 1:30 hours for less than 100 grams.
The Instruction Manual has been updated and is marked February 10, 2013. For your convenience, the changes are only on page 14 and 29 (the quick-reference firing schedules)
Very thick pieces fired this way with full sintering, no distortion, and no cracking. They were fired in two different kilns, so it seems that with the one-step firing schedule White Bronze is not so sensitive to slight changes in temperature.
The following pieces are 13 cards thick – 10 cards a piece plus a 3-card bail on the back:
To test the brittleness of these piece I made a circle of the same width. Here it is next to a penny:
I threw it hard (not just dropped) a few times on a concrete ground and it did not break. Don’t get me wrong: this is not a good way to test your pieces! Although people report that they regularly tumble White Bronze without breaking it, White Bronze is still more brittle than the other clays, and cannot be hammered, bent, or drilled. The test is always to sand it with course-grit sandpaper (150 or 220) and see if it becomes all metallic or has pits of powder. You will never be able to perform the finishing process if the piece is not well sintered.
It seems that thick pieces are less brittle than thin ones. However, if you are still worried about strength, here is a way to protect a piece. For the following piece, a frame of copper was fired first at high-fire schedule. This is the structural part of the piece.
1. Cut 3 identical-size shapes. Leave one of them solid (6 cards thick). In the second (2 cards thick) cut another, smaller, identical shape. In the third (4 cards thick) cut a smaller, identical shape.
2. Place the second layer on the solid one.
3. Place the third layer on the second one. You have now created an undercut, an empty space between the first and the third layer.
4. Seal the gaps between the layers.
5. Insert fiber paper into the undercuts to keep them open during firing.
6. Fire the piece following high-fire schedule for copper.
7. Clean the undercuts and much as you can. Press White bronze into the undercuts to fill them completely. Dry.
8. Roll a layer of White Bronze, 1 card thick. Lay it on the copper piece.
9. Cut away the excess clay from around the inner frame. Dry.
10. Make your piece as if the White Bronze were the backing layer.
11. Fire following the new low-firing schedule.
Notes:
- The moon in the window is made with Brilliant Bronze, which sintered just fine at this low temperature.
- The frame can be made from any other clay. Here is a piece made with Low-shrinkage Steel XT and White Bronze.
Why is the undercut necessary?
First, high-fire metals may not fuse to White Bronze at low-fire schedule. The undercut is a mechanical device that prevents the metals from separating.
Second, the White bronze pressed into the undercuts prevents the inner (White Bronze) part from shrinking away from the frame.
And last, just for color comparison, here are similar pieces side by side, one with White Bronze, the other with Low-Shrinkage Steel XT.
Both pieces above were fired with one-phase firing schedule, no pre-firing.
Both pieces required pre-firing, since a large amount of copper is involved.
February 10th, 2013 at 4:04 pm
Hadar, thank you, so If we are firing only once, then would we embed the white bronze between two layers of carbon? My pieces are not sintering at 1325 degrees either, so I will increase by 10 degrees!
February 10th, 2013 at 7:20 pm
Awesome! Thanks for the updates 🙂
February 11th, 2013 at 8:30 am
Sandra, Yes, pieces all covered with carbon.
February 11th, 2013 at 8:56 am
Hadar, on page 14 you say “Ramp at full speed…”, whereas on page 29 you say, “Ramp at 1800〫….” Also, there is a typo in the lower left box on page 29. You have 700〫 when I believe you mean 1700〫 . Sorry, it is the perfectionist in me.
February 11th, 2013 at 10:10 am
Thanks, Ron. It’s being corrected right now.
February 11th, 2013 at 11:07 am
Hadar, As always, thank you for always being on the cutting edge and keeping us all so informed. I’ll be teaching some employees of the Paragon Kiln factory a class using your clay in a few weeks with some of your other clays. Now I think we will also do some pieces in the White Bronze since we will have a shortened firing schedule. Keep up the great info on the Blog! Am looking forward to taking your Color Patterns in Hollow Forms Workshop with my daughter in Texas this spring! Julie
February 11th, 2013 at 11:08 am
Thank you Hadar – I just fired some Low Fire Steel XT using your new single firing method. I love it. One quick question regarding “baby oil” soaking the steel to prevent rust is this only if you leave the fired steel xt in it’s original color?
February 11th, 2013 at 12:15 pm
Yaaaaaaaaaaay!!!!! All my fellow Hadarians will be thrilled!! :). Very exciting!
February 11th, 2013 at 4:16 pm
Christy Ann, you can also seal it from the outside with long lasting lacquer spray. I find that baby oil or any scented oils work great.
February 11th, 2013 at 10:03 pm
Yea I will drag out my white bronze. I have found thicker is less brittle.
A quick question I have a brick kiln with no venting hole and since I was doing all my first phase firing on the stove but should I now consider adding a vent hole? I have attached a link to my kiln which has a little peep hole in the front with which can have a hole added. What do you think?
http://www.riogrande.com/Product/Rio-Model-1000-Enameling-Kiln-with-Nine-Program-Controller/703121?pos=2
Thanks
Cindy
February 12th, 2013 at 9:20 am
Cindy, A top hole is better than a side hole. You can easily drill an eighth inch hole in your brick lid. It’s very soft.
March 9th, 2013 at 3:41 pm
I was very excited to hear this news, so I immediately fired some white bronze at the suggested temp but they didn’t sinter properly in my kiln. So I re-fired the piece I didn’t break (intentionally) at a high temp and held for 2 hrs. It worked, but I forgot exactly what I did. SO, I will now take it step-by-step, including photos. I’ll be firing one piece 4 cards thick and one 9 cards thick. I did let them air dry overnight. Of course, the 4 card piece warped a bit. I put it into the frig and then placed a coin jar (heavy) over it for a couple of hours – didn’t flatten – I would’ve, that jar is heavy! I decided to try steaming the piece a bit (just made some hot water for tea) and then put it back under the jar – it worked. I will be teaching a class on white bronze in May at a bead store, the new firing schedule has encouraged me and the response has been fantastic!
April 5th, 2013 at 12:46 pm
What is the best way to clean white bronze after firing? I’m worried tumbling will break delicate pieces but sanding, pro polish, and taking a steal wool pad is just not getting the job done….please help!
April 5th, 2013 at 4:26 pm
Jennifer, Please see the file “Finishing Fired Metal Clay” on the right panel of this blog.
October 23rd, 2013 at 6:12 am
Hi Mrs Jacobson,
My question is for a ring white bronze wich size before firing? I did not find it on your blog. Thank you for anwsering and excuse my english I’m from Québec province.
Chantal
October 23rd, 2013 at 8:43 am
Chantal, White Bronze is not strong enough for a ring. This is why it is not on the shrinkage chart.