Monday, June 30, 2008

Upcoming raku firing

I will be breaking in my new raku kiln Thursday. It's a garbage can kiln. Can't wait.

I will be using a copper matte glaze. I have seen this glaze or variations in a couple place. Several books and the best place was in a gallery, on a little note card next to some spectacular raku vases. I've never gotten this glaze to work for me. However I think the issue has been my raku technique - firing in an electric kiln then walking the pots outside into a reduction can.

Amount Ingredient
36 Copper Carbonate
36 Copper Oxide--Black
16 Frit--Ferro 3110
8 Iron Oxide--Red
4 Cobalt Carbonate

100 Total

I make a couple changes to the original, I add 2% magnesium dioxide to encourage purples. and I am dropping the RIO by 2% as I use an iron bearing earthenware for raku.

36 Copper Carbonate
36 Copper Oxide--Black
16 Frit--Ferro 3110
6 Iron Oxide--Red
4 Cobalt Carbonate
2 Magnesium Dioxide

100 Total


I'm not sure if I am adding too much magnesium but we'll see. Raku is - from my perspective - much more difficult to develop glazes. Many more moving parts; did the pot cool too much, not enough before going into the reduction can? What is used in the reduction can, newspaper or pine needles? There are dozens of variables to take into account. Raku glaze development is much more shotgunning it while wearing a blindfold.

Saturday, June 28, 2008

Bisque firing today

Just a quick post today.

I bisque fired today. I'll unload tomorrow. I am planning on a raku firing in my new homemade raku kiln Thursday night. I'll post pictures. I am also going to try to squeeze a couple test batches of glaze in this week.

I saw some really cool pots today at the gallery store in the Seattle Center. If I get time tomorrow I'll post more about them.

It was a great day to be out and about and tomorrow is a yard work day.

=)

Friday, June 27, 2008

Red pots... Martian red

So my other interest besides pottery is astronomy. I was a physics major in college. Imagine my surprise when I realized my two very disparate interests converged today.


The soil on Mars very similar to Earth's soil.


So naturally my first thought wasn't about life on Mars but... what about Martian clay? Someday... someday someone will make pots of Martian clay. Someday someone will test fire Martian soil.

At first I was giddy thinking of what cool wonderful exotic glazes. But then my geeky science d0rk came through. The chemistry is the same. Even if the trace elements are in a different balance it's not like there are undiscovered elements in the dirt on Mars. In reality Martian clay, glazes would be the same as regular glazes and clays. Maybe some naturally saturated with certain elements. Possibly some mixed with elements that are scarce or not common in soil here but frankly nothing that we couldn't make here.

Still ... I wonder how long until someone makes a pot with Martian soil.

I get back into the studio tomorrow and will fire my test tiles.

Thursday, June 26, 2008

Details

A bit on how I test glazes.

I use extruded rectangular tubes. I hand cut them into roughly 4 inch heights. I put one hole through the test tile - just in case I want to hang it. I have a little seashell that I press into one side.

I always use porcelain for the test tiles. I usually work in porcelain so that helps. I usually want to see the glaze on porcelain. I do some work in a real nice red iron bearing stoneware but I never use it for test tiles. Yeah, I know the clay really impacts the glaze. I have a couple glazes I really like that only look good on the iron bearing stoneware. But also... I am a bit anal and a little lazy. I hate getting the red clay on things that the porcelain uses, like the extruder. If I made stoneware test tiles I'd have to clean the bejeezus out of the extruder and I am too lazy to do that so I just make porcelain test tiles.

I generally make a 300 gram batch when testing a base. I'll mix 300 grams of dry with 200-300 grams of water. I sieve the batch through an 80 mesh sieve twice. Then I dip the test tile in the glaze and fire at cone 6 in one of the electric kilns in the studio I work in.

I usually use witness cones. From using the witness cones the kilns fire about high 5 or low 6. The cone 6 witness cone usually just bends, about 15-20 degrees.

The kilns all have kiln sitters. No computer controlled kilns. Yet. So no soaks. No slow cools.

I have 50+ test tiles drying now. I am going to bisque fire them Saturday morning. So maybe some glaze test firing next weekend.

Wednesday, June 25, 2008

Developing a Fake Ash base glaze

I love Steven Hill's pots. Specifically I love his glazes. His fake ash is delicious. I aspire to have glazes as wonderful as his on my pots. I don't want to simply cut and paste other people's work though. I want my glazes to be my own.

There's nothing new in pottery. Pottery has been around literally as long as man. Virtually nothing I will do hasn't been done before.

These two opposing paradigms are what we all need to balace in developing our own glazes; something wondeful and new yet you can bet your ass someone has done it first. Even if you don't copy someone else you're probably not the first one to do whatever it is you're doing. Such is the world of potting.

I am working on finding a base fake ash glase. I am looking for a fake ash glaze that works well on both stoneware and porcelain at cone 6 in an oxidizing electric kiln. Further I want a fake ash glaze that takes color. I have visions of a red fake ash... or a purple. In order to do this I need to find something that will color a glaze overloaded with calcium red or purple. Off hand I don't know what I need to do.

I am starting with two base recipes.

Via Ceramics Monthly Satori Yamaoka's synthetic ash:

Magnesium Carbonate ........................ 6%
Phosphorus Pentoxide ........................ 6
Whiting .................................................. 63
Potash Feldspar ................................... 12
Kaolin .................................................... 10
Silica (Flint) .......................................... 3

I am swapping out the Phosphorus Pentoxide with Bone Ash.

Magnesium Carbonate ........................ 6%
Bone Ash ............................................... 6
Whiting .................................................. 63
Potash Feldspar ................................... 12
Kaolin .................................................... 10
Silica (Flint) .......................................... 3

This recipe is originally listed as cone 9. I am working at cone 6. In order to get this to melt properly need to drop the melting point. As a starting point I am going to swap the Potash Feldspar with Neph Syn.

Magnesium Carbonate ........................ 6%
Bone Ash ............................................... 6
Whiting .................................................. 63
Nepheline Syenite ............................... 12
Kaolin .................................................... 10
Silica (Flint) .......................................... 3

The resulting analysis:

Unity Oxide
.025 Na2O
.008 K2O
.099 MgO
.868 CaO
1.000 Total

One thing about this one I notice long before I put on the mask and mix it is that it does have what I would expect as the high enough percentage of CaO to be a good fake ash glaze. I am not sure if this will melt and flow at cone 6. If not my next step will be to add some lithium and possibly increasing the amount of bone ash.

Next since I have a man crush on Steven Hill's glazes I am starting with his fake ash glaze via John Britt's aswesomesauce book "The Complete Guide To High Fire Glazes"

Feldspar--Kona F4 ... 6.8
Dolomite ..................... 3.8
Whiting ....................... 45.5
Kaolin--EPK ............... 30.3
Silica ............................ 13.6

Total ........................... 100

Bentonite ................... 2.3

Like the Yamaoka's glaze this was designed for high fire and I am working at cone 6 so I need to drop the melting point. I am less sure of this conversion and will probably have to try several iterations of this. First lets trade the Feldspar for F3134.

F3134 ......................... 6.8
Dolomite ..................... 3.8
Whiting ....................... 45.5
Kaolin--EPK ............... 30.3
Silica ............................ 13.6

Total ........................... 100

Bentonite ................... 2.3

I don't think this will be enough to drop this to cone 6 runny goodness. I am going to add some lithium, 3%.


F3134 ......................... 6.8
Dolomite ..................... 3.8
Whiting ....................... 45.5
Kaolin--EPK ............... 30.3
Silica ............................ 13.6
Lithium Carbonate .... 3

Total ........................... 103

Bentonite ................... 2.3


Unity Oxide
.072 Li2O
.006 Na2O
.002 K2O
.042 MgO
.878 CaO
1.000 Total

I will normalize this to total 100 again if this works. Otherwise I am not wasting my time. Not that the math is hard, it just a waste of time if this isn't the final version. I only want to do it once.

So those are the recipes I am going to test. I'll add some cobalt to each batch because I tried testing a fake ash glaze one with no coloring agent. It's a challenge.

Tuesday, June 24, 2008

First!

How did I get here? Starting a blog about working with clay and glazes...

I decided to start a blog to help with several goals.

First; I want to be a better potter. This means a multitude of things to me. I want my glazes to be as good as John Britt's or Steven Hill's. Not a copy of their glazes but as good, as wonderful as Hill's fake ash and Strontium Crystal Magic combination. As unique as John Britt's oil spot glazes. I want my pots to be useful, eye catching, and expressive.

While I have a long long way to go on my journey to make pots I am truly happy with (when I look at my pots I generally just see the flaws) I also want to transform my money sucking hobby into at the very least a break even proposition. I want to make some money from all the time, money, blood, sweat, and electricity I am sinking into my pots.

In my pursuit of these two goals I find myself thinking that I am probably not alone. Ok, there may be only a handful of people who are also looking for great glazes and refining their pottery techniques but I am probably not the only one. Also I do better when I write it down. When I have to explain what I am doing to someone else, even if nobody ever reads this. Someone could so I need to think things through. Writing this helps me achieve my goals.