Monday, January 8, 2018

Knowing when to stop! A good Firing. Urns.

I find the last few minutes of a firing the most stressful, the Big question is knowing when to stop. I like to plan for the last hour of a firing, and think about how long glazes will need to mature, and how fast or slowly the temperature in the kiln should be rising. I try to think it out before the firing begins, but firings are dynamic, and firing with wood is something of an art as well as a science.

It would be nice to be able to open the kiln door and examine the pots like pies in an oven to see if they are "done", but the kiln is holding an atmosphere, white hot with just a faint yellow tinge, that is almost as bright and as deadly as the sun. Inside may look inviting, but it is not a friendly place, there are no happy aromas of hot pastry, braised beef, and sautéed onions!

Through welding goggles I can carefully peer at cones that are incandescent with heat, and await their bending and fall. I can sometimes glimpse the curve of a pot, the frozen D of a handle, but a glimpse is all. So I consult my graph paper log of the firing, noticing the dotted steps of each temperature reading as hour by hour the temperature rises. I time the fall of the cones, and I try to even the heat from top to bottom of the kiln, pushing in the chimney damper a little to slow the passage of heat through the kiln to the minimum needed to maintain a rise in temperature and an atmosphere in the chamber that is a little starved of oxygen.

Eventually I have to make the call to stop stoking. The top of the chamber gets hotter than lower down, so there is a compromise. If I try to get the lower part of the chamber up to an ideal temperature, than the top can be over fired. If I stop when the top is only just up to temperature, then the lower pots will be under fired. I have made some allowance for the expected temperature difference by selecting glazes that will love high temperatures for the hot part of the kiln, and ones that will tolerate lower temperatures for the cooler areas, but each firing is a living thing, and requires a judgement call.

I have some important pots in the upper part of the kiln, one is a commissioned piece, and there are some related pots as a back up in case the commissioned one turns out badly and we need a "plan B"! When the top shelf gets to cone 11 half down, I have to stop the firing for the sake of those large pots, even though the lowest pots will be under done. I know that I can re fire the pots that haven't quite got there, but it is hard to salvage a badly over fired pot!

The kiln was ready to unload on the third day after the firing, and Peter Watson, the friend who gave me my first lessons in potting and encouraged me along the way, stopped by to see the kiln unloaded.

The neighbour's -not quite our cat- cat who had helped me fire the kiln also watched with some interest.

Urn. 11 1/2 x 8 1/2 inches (292 x216mm)
The commissioned pot is a funeral urn. It was quite a responsibility to make such a special thing, and I wanted to make it simple and thoughtful. On an overcast day, the glaze seems sombre but there is a great deal of beauty when the sun lights it up.

Urn, detail of the lid.

We were very pleased to see that the urn was a success and it was well received by its owner when he picked it up yesterday.

There were some under fired pots as predicted that will go back in the kiln, but there were some treasures amongst the ones that got to temperature. In all it was a good firing!

Bowl with copper red glaze. 6 1/2 x 3 1/2 inches (165 x88mm)
Copper red bowl detail.

Vase. Ash glaze over Shino. 5 1/2 x 5 1/4 inches (140 x 133mm)

Vase. Detail. Note the crystals over the ash glaze.

Urn. Ash glaze over Shino. 11 x 6 1/2 inches (280 x 165mm)

Urn. Detail of lid.

Breakfast bowl. Tenmoku glaze with rutile over glaze. 5 1/2 x 2 3/4 inches (140 x 70mm)

Breakfast bowl. Detail. Note the pollen-like sprinkle of golden crystals.

Breakfast Bowl. 6 1/4 x 2 3/4 inches (158 x 70mm). Same glaze combination as the previous bowl.

Urn. Thrown and altered. Rutile over Tenmoku glaze. 10 1/2 x 10 x 8 inches (267 x 254 x 203mm).

Urn. Detail.

Urn. Rutile over Tenmoku glaze. 15 1/4 x 7 1/2 inches (387 x 190mm).

You may have noticed that there were several more urns! When someone commissions me to make something for them, I usually make several related pots. I think with my hands, and prefer to try to give the pot form in clay from the beginning. Other potters are happy to draw out ideas on paper, or even use 3d software on the computer to solve design problems. Really we need to find our own way to solve these things, paper or technology is good for some, clay for others, we are individuals!

Enough for now! I will be getting back to the wheel again this week. Hope to make coffee mugs, pouring bowls, a large mixing bowl for baking bread, and .... maybe some little tiles.


gz said...

Tasty Pots!!
Timing can be SO critical with crystalline glazes

Linda Starr said...

oh that red bowl, wonderful to see your hard work to completion

Peter said...

Hi Gwynneth,
Lovely to hear from you (goodness you were up late!). Yes timing is critical Especially with crystalline glazes!!!

Hi Linda,
Good to hear from you. Mmmmm it is a yummy red!

Anna said...

Hi Peter a great post on the vagaries of firing with wood.. the urn glaze is very interesting and the copper red is not as maroon as some, very nice.

Peter said...

Hi Anna,

Thank you! It was the first time I had used the glaze combination that I used on the urns on something so large, and it was interesting to see it on a bigger scale. The rutile glaze has great potential and I am looking forward to playing further with it!

Mayra Peralta said...

All your work looks wonderfull. Today I returned to find your blog. I really appreciate your post about Chun glaze. Greetings from Mexico. Keep reading����������

Mayra Peralta said...


gz said...

They will keep on broadcasting most tv programmes that are worth seeing, FAR too late!!

cookingwithgas said...

Looks like a great firing, I think you called it well.

Arkansas Patti said...

Loved that copper red bowl. I fear as a non potter that I was guilty of thinking firing was like baking bread. I stand corrected.
How nice that your mentor is still in your life and interested. He knew what he saw in you.

Melissa Rohrer said...

Some great ones!

Peter said...

Hi Mayra,
Very nice to hear from you all the way from Mexico. Happy New Year to you! Glad you enjoyed the Chun glaze post!

Hi Gwynneth,
Yes the TV does its best to make us nocturnal! Maybe it is all part of some dastardly plot!

Hi Meredith,
I was still smarting from a firing I did in November when I called it wrong and over fired! It was a good education!

Hi Patti,
I think that some of the bread I bake thinks that it is pottery.... a rock-like crust that has a hollow centre! :-)
It is lovely to still be in touch with Peter W. who gave me a start with clay!

Hi Melissa,
Thanks for the encouragement!

Anonymous said...

Hi Peter, lovely, lovely pots! Congrats on your success, you have worked for it and are very deserving!

I wanted to pass along my review of a wonderful clay formulation class I recently completed. I've been working with clay for 25 years and really never knew that much about clay and it's formulation. I've learned so much! The teacher is Matt Katz, the class is on-line, and there was a potter from Darwin in my class as well as a Canadian and a Dane in addition to some US residents. Truly a fun group and a lot of knowledge was shared.

Cheers, Owen in Oregon

Here is the review:

I don't share this with any desire to bring attention to myself, I just wanted others to know about it in the hopes that it may prove helpful in their development as potters. Thankfully it never ends!

Peter said...

Hi Owen,
Thank you very much for your encouragement and also for letting us know about the review that you have written about the clay formulation class that you recently attended. It is a really interesting review, and I was delighted to hop over to your site and have a read, and hope others do the same!

Best Wishes,


Anonymous said...

Thanks Peter! I can honestly say that it’s a whole new ballgame for me now, after 25 years of working with clay including full time for the last 10. It’s so exciting! Cheers, Owen