Sunday, February 28, 2016

February At The Old Post Office, (Part Two)... A Bowl, getting up close and personal!

The process of making a pot or bowl on the potter's wheel is a physical one. The object is brought to life through the potter's hands and fingers. Centering, lifting, shaping, forming, coiling, collaring, smoothing, cutting, joining, the process of making is described by "doing" words that are expressive of physical effort and touch. My favorite ceramic objects are usually ones where the potter has not turned the piece excessively with a metal tool, or smoothed away all evidence of having been made by a human hand.
Throwing demonstration at the Otago Museum in 2015. Photo Rhonda Beck.
I am most likely to enjoy pots that have had their glaze applied in a rather active way by pouring, splashing, dipping, or brushing. I like areas where glazes overlap, or sag, or run, and it is nice to find little marks near the foot of a pot where the potter has gripped it whilst glazing. I think these touches of humanity should be even more highly valued in a world where so much of our domestic ceramics is stamped, pressed, or squirted out of a machine and glazes sprayed or printed.

Imagine how boring it would be to a visit to an art gallery if all the paintings in it had been airbrushed, if your favorite Monet, Rembrandt, Frans Hals, De Kooning, or Bonnard, had no visible brush strokes and their canvasses were flat and smooth!

One of the pleasures of handling hand made pottery is being able to pick up the item and feel weight, balance, and texture. This pleasure is denied to the viewers of blogs... so we will just have to rely on the eyes and some imagination.

I thought I would introduce you to a porcelain bowl that I glaze fired part way through February. The bowl was probably around 15 1/2 inches (393mm) when wet and slimmed down to about 12 3/4 inches (324mm) in diameter when fired. Porcelain shrinks a great deal when it is fired because it becomes glassy and vitrified. visualize of a pile of powder mysteriously turning into a puddle of liquid, and you will see what I mean. This makes porcelain strong, non absorbent, and translucent if thinly thrown, but the extreme shrinkage makes it hard for the potter to visualize the final size.

The bowl has a deep foot underneath it that I added when the bowl was leather hard and still a little pliable. There are a number of ways of adding a foot to a bowl, one is to leave the base very thick to start with and then to remove surplus clay with a loop tool, another would be to throw a little cylinder of clay and add that when the bowl and the cylinder are leather hard, but, when making a deep foot ring on a large bowl I prefer adding a coil of clay, centering it, then throwing the coil to its finished size. I sometimes cut out little half round openings in the foot with my cut off wire.

I used 4 glazes on the bowl, and I applied them by pouring. I hold the bowl in one hand, and pour glaze from a small saucepan full of glaze that is held in the other hand. I do this over an old metal Wok, which usually succeeds in catching most of the run off glaze!

The first to go on was BTM (black tenmoku)
This is a saturated iron glaze that gives a lustrous brown black when fired to a high enough temperature. I like to fire the top part of the firing slowly when using this glaze, and hold the kiln near the peak temperature for half an hour or so.

Over that went a good splash of a Janet deBoos clear glaze (number 144 from her first book) that I modified by adding rutile and copper carbonate. This gives a nice pale green glaze over a white clay, or a variable optical blue when over a dark glaze or clay.

Over that went AV1 which is a dolomite matt glaze that gives a smooth, slightly oily feeling glaze when used by itself on a pot. Over a saturated iron glaze it gives lacy patterns which vary a great deal depending on how thickly this glaze is applied.

Finally I poured on a splash of a saturated iron glaze that gives a lustrous red. This is based on a recipe that may go back to the Chinese Song Dynasty. I found it in a 1997 Ceramics Monthly article about a wonderful potter from Taiwan called Wang Chun Wen.

The bowl was fired to cone 10 in an electric kiln. The firing was done slowly near peak temperature to give time for the glazes to mature and intermingle nicely.

Cone 10 Glazes used: All fired in oxidation in the electric kiln.

55  Nepheline Syenite
15  Talc
15  Wollastonite
10  Ball Clay
15  Silica
8  Red iron oxide

DeBoos glaze 144 Cone 9 - 10 (modified)
40  Potash Feldspar
25  Silica
15  Whiting
10  Ball Clay
5  Zinc Oxide
+ 3  rutile
+ 2  copper carbonate

AV1 cone 10 a high magnesia/alumina silky matt glaze probably best in reduction.
34.7  Potash Feldspar  
19.6  Dolomite
3.1  Whiting
23.6  Kaolin  
18.9  Silica

Wen/Conrad translation of Chinese recipe. I modified this (the original called for 10% red iron oxide and 4% Edgar Plastic Kaolin, I added 9 % yellow ocher to supply some of the iron, and all of the clay to the recipe. I also adjusted the silica and feldspar amounts to take account of the change of clay.).

47  Potash feldspar
10  Bone Ash            
8  Talc                      
17  Silica                      
9  Yellow Ocher      
8  Red Iron Oxide    

The original Wen/Conrad translation was as follows
48 Feldspar
10 Bone Ash
8 Talc
20 Silica
4 Edgar Plastic Kaolin
10 Iron Oxide


Anna said...

Hi Peter
that is a gorgeous glaze combination that works so well in a reduction firing. Very generous of you to put up the recipes too..

Melissa Rohrer said...

Beautiful effects on the bowl. I find I enjoy the immediacy of clay and am more likely to leave the throwing marks than not. And I used to be very particular about glazing. Now I am delighted if some inside glaze spills over the side onto the outside glaze...etc. Happy accident!

Peter said...

Hi Anna,
Good to hear from you. Always happy to put up glaze recipes, it is nice to see them being used. Just a quick correction... the bowl was fired in Oxidation. I did say somewhere that the AV1 glaze is probably best in reduction which might have confused you. In fact all the glazes should work well in reduction, but would give a different looking result.

Hi Melissa,
Nice to hear that you embrace happy accidents too! It is taking me quite a long time to feel freer with throwing and with glazing (it is such a struggle to get these things right to begin with!!), my instincts are for freer work, but I can be too self critical to let it happen!

Michèle Hastings said...

So much happening on that beautiful bowl. Thank you for the reminder of the thrown foot ring. I haven't done that in a long time.

Arkansas Patti said...

So agree with you on the human touch. Perfection reeks of machinery, not artistry.

Peter said...

Good Morning Michèle! Sun's up here and I am groggily checking emails and waiting for a second cup of coffee to do its work! Lovely to hear from you. Thrown foot rings are fun, although I don't do a lot of them myself. I think they may have some advantages on shallow and wide porcelain bowls like this one, in that I was able to give good compression to the clay in the base of the bowl when making it on the wheel because I did not have to allow a thick pad of clay for hollowing out a foot. Also I have the feeling that a deep foot with some openings around it helps get the heat of the kiln under the bowl as well as over it which is hard to do in an electric kiln with no real air movement if the bowl sitting right down on the kiln shelf.

Hi Patti,
Lovely to hear from you. We do live in strange times where we are surrounded by so much stuff that is machine made and has no humanity at all. I think that birds have the right idea, in that they raise their young in nests that they have made themselves. I was particularly fond of a pair of blackbirds that we had here one year, they made their nest in a dense tangle of a black current bush that I had planted and let go a bit wild. I often think their young had a great start to life with all that healthy fresh fruit and vitamin C!!

Anna said...

Hi Peter I looked at that bowl and thought Reduction Firing and so my mind skipped over your detail where you said it was an electric (oxidised) firing.. very impressive.

Peter said...

Hi Anna,
Thanks for that, my first thought was that I had probably written "reduction" by mistake as I was very tired when writing the blog post having been up at 2 hour intervals all night checking my kiln and had written the blog post to keep myself awake whilst waiting for cones to go down! :-)

Anonymous said...

Gorgeous glaze interactions. For the past couple of years I've been using that same technique of adding a foot ring by throwing a coil onto the pot of my platters. People get puzzled because they can still see the marks on the inside of the base where it was wired off the wheel, but that is inset into the foot ring. The only issue I've come across is that the coil is wetter than the platter and I have to remember to bag the whole thing up and let it equalise slowly. I've had a few cases of the ring cracking at the joint to the pot where it shrinks more than the leather hard pot. It's so much easier than turning the bases out of large platters though.

Peter Gregory said...

Hello Mike,
Good to hear from you. It is nice to have a few puzzles for people to solve, I wonder what imaginative theories could be arrived at to explain the wire marks on the base of the pot! I can see that the wetter foot ring could be a problem. I have tended to add it at an almost too early stage when the bowl is slightly softer than ideal and haven't had problems with the joint cracking whilst drying, but have sometimes deformed the base of the bowl through it being too soft. Bagging the bowl up to equalize drying is certainly a good idea and would allow for doing the foot ring when the bowl is stiffer. I do like the look of a deep foot ring, and there are all sorts of creative possibilities too.

Linda Starr said...

unbelievably beautiful and love the foot ring.

Peter said...

Thank you Linda :-)

angela walford said...

hey peter, awesome glaze layering! I think the cone 10 is the gem still ;) I do like getting that body strength... sorry to read about your shoulder injury, I can sympathise as I'm just on the other side of one of those injuries...hope yu get the help yu need! I ended up going with the cortizone injection, which has fixed it the best, cheers ang

Peter said...

Hi Angela,
Thank you for your helpful comment. I've been reading quite a bit about cortisone injections and worrying a bit about whether or not it was a good thing to do if it is offered to me. So it is good to hear that it has been helpful to you :-)

gz said...

A lucky and beautiful run on that foot!

Peter said...

Thanks Gwynneth, it is those little blessings that make it all worthwhile!