Dots.... Onwards in the Quest

Well, I'm still working on the dots problem. For a day or two I actually thought that it might be due to over-firing as the shelf with the worst case of the dots was definitely over-fired, but then reality set in.

I fired another load of maiolica-type work and made sure to have witness cones on every shelf. This confirmed that the bottom of the kiln was over-firing. I debated switching the top and bottom thermocouples but in the end didn't and just went back to my old system of having a deep space on the bottom and shallower spaces higher up the kiln, and placing a kiln shelf right at the top. I also went back to leaving the top peep hole open. Don't ask me why this works, but for me it does. Maybe my kiln vent is just weird, but it worked before with the manual kiln and is working again now with this computer-controlled one. The original thermocouples gave a very even firing, but this second set clearly doesn't. So I at least learned that much. The firing was much more even.

But dots appeared on every shelf.

Then I sent an SOS out on Clayart, a list I belong to. This list (if you aren't on it, you should be) has some super helpful and knowledgeable people on it, and I got a number of responses. Some of the suggestions made were: could be the opacifier; fire the bisque higher or longer to be sure it is well cleared; re-screen the glaze; could be the clay; could be a change in glaze material; try another glaze; fire slower.

I tried re-screening the glaze first. Easiest thing to check! This had no real effect except that I did realize that the thickness of the glaze slurry had drifted and it needed more dilution. I mix large batches of this white glaze, keep it in a laundry tub for dipping large pieces, and just add to it whenever the level goes down too far. That doesn't mean it doesn't get screened except when being mixed, though. I periodically re-screen the whole batch. The frit (F3134) is somewhat soluble, and I think it gets used up differentially. So I sometimes add a titch of frit and that means re-screening and testing. Plus the glaze sometimes develops tiny granules. They dissolve when I touch them, but I figure they can't be good so when I see more than one or two on a glazed piece, I re-screen. But in fact this glaze had been standing more than usual lately, because I have been making stuff in a couple of plain colours in order to have lower-priced pieces to sell. So it made sense to try that first.

Unfortunately, as I said, that had no effect.

I couldn't really try a different opacifier. I have been using Superpax and it is not a new bag. Tin Oxide has lots of problems, not the least of which is that it is expensive. So I don't want to get into that. Plus the small amount I have has crystallized badly....

I tried a slower, slightly higher bisque. This had no noticeable effect either. One problem I have, my Studio is in a rural area, and our electric current fluctuates. We are supposed to have 'time of use' pricing, that is, hydro is supposed to be cheaper during the off-peak hours. I have tried firing at night, but have found that the firings take longer so I'm not sure I'm ahead at all. I've tried to talk to my hydro supplier, but they don't talk to humans. Long story short, my bisque firings, all on the 'slow bisque' program my kiln has, vary between 8.5 and 14 hours. That's not particularly fast. Still, I tried a cone 05 firing to see if it made a difference, but it didn't seem to.

None of my glaze materials are new, and none are particularly old, or have gotten damp or frozen or any other such thing.

Yes, I have changed clay. But I changed clay months ago, and for three months there were no dots. No pinholes, no bubbles, no dots.

I really don't want to change to a completely new glaze. I could try my clear glaze with opacifier, but it doesn't take the colours nearly as well as my white one does.

And fire slower? How can I when the current fluctuates so much? I can program to my heart's content, but if the elements don't get the power they need, they are going to slow down. Glaze firings also vary a lot, everywhere from 6.8 hours to 12.6. I log every firing, so I know.

So what to do? Well, I tried two things in the latest load: a batch of glaze with 3% more frit 3134, and a batch with 2% less Superpax.  I dipped a mug, new clay, slow-bisqued to cone 06, in each, plus one in the large glaze batch in the tub.

Here is the result. They were all on the same shelf in a well-loaded but not tight, kiln. The witness cone is nicely bent over, tip touching the little plate I put it on. The firing to cone 6 took 8.51 hours.

The left-hand mug, with the tomatoes, is the glaze in the large tub. The middle one, with the peas showing, is the low Superpax version (it is slightly less white), and the carrots are the higher frit version.

NO DOTS!

Boy, am I confused now.

 Well, guess I'll go drive the garbage out to the road for tomorrow's collection - they come so darn early I have to do it the night before and hope the critters don't get into it, ravens or racoons or skunks or the neighbour's dog - and let my subconscious work on the problem overnight.

Dotty Update

One thing about pottery, it is not quick. Just figuring out what happened to cause all those 'dots' I talked about last post took me a week, and I was lucky  it was only one week. I found the problem right away.

I re-fired several of the mugs, each on a different shelf in the kiln. I made sure to have large witness cones near each one.

Bingo.

The bottom shelf was almost a full cone over-fired. The witness cone for Cone 7 was fully over. The other shelves were the Cone 6 as I expected.

So I'm figuring the problem is the thermo-couple at the bottom of the kiln. This problem of 'dots' has been creeping up on a me a bit so I guess the thermo-couple has been failing gradually. I just didn't twig to the fact that it was always the pieces on the bottom that were acquiring a 'dotty' nature in the firing.

Well. Lesson learned. From now on I will put in witness cones at least every 3rd or 4th firing. I've been slack about that. They tell you to use them every firing, but with a computer-controlled kiln it is hard to convince yourself to actually do it. Especially in really full loads.... and especially when you stop to think of how much those darn things cost.

Re-firing didn't affect the dots, by the way. They neither got worse nor got better. And I even tried applying dabs of colour to the dots and re-firing and that didn't work because I couldn't get enough on to really cover the white.

Another learning experience.... if I learn from my mistakes, I'm going to be awful smart some day.

Problem-solving

Yesterday, I wandered into the Studio early, coffee cup in hand. It was Sunday and I used that as my excuse for not planning to work as usual. I'm old enough to remember when Sundays were Sundays, and sometimes I still use the day as an excuse to do what I feel like doing instead of what I should be doing. I had the vague idea that I'd look over some of the challenges I've been working on lately and maybe there would have been a miracle overnight, or else there would be some sort of inspiration, maybe a flash of light, a drum roll, a voice from above, something like that, solving my problems for me.

No such luck. The travel mugs I'd so looked forward to seeing out of the kiln on Friday were still 'spotty'. This is a problem with low-fire majolica, but sometimes I see it on my Cone 6 stoneware too. Usually I just see one or two tiny white dots, but in this case every mug has lots wherever there is colour.

All the mugs suffered from severe 'dottiness'. (Usually it is just the potter who suffers from 'dottiness' around here.) They had all been on the bottom shelf in the kiln.... none of the pieces on the higher shelves seemed to have any dots.... so, my guess, it must be that the bottom shelf was slighter cooler than the upper ones. Or hotter, or the vent system didn't affect it the same, or I put too much colour on the mugs or any other ideas?

Another problem looking for a solution is a little oval soap dish. We won't discuss the fact that this is a commission and I didn't insist on charging my usual development fee. Should have, then I wouldn't have to be futsing around trying to make very small oval dishes with closely matching lids. The customer was absolutely adamant about the design, the size, the shape, the weight. He had worked hard to get to my studio and I didn't have the heart to say 'no', but I should have.

 Now, this would be dead easy in a round shape, but the customer wants to match an oval one he has. It is less than 4" long and weighs practically nothing. Earthenware, slip cast, decorated with a decal.... what was I thinking to even consider this?

I make my slab pieces over plaster molds.  Lots of people make theirs into plaster molds, but I find that then I have to make a template, cut the clay carefully, ease it into the mold and try to shape it without making thick corners.... my system is easier, more flexible, less annoying and usually works great. I also like the fact that I can change the edges of the dish more easily. But the trouble with this little thing is that it warps in the firing.

If you look carefully, you can see that the top piece doesn't sit quite down on the bottom piece near the middle of the long side. And the two pieces were fired together.This is my third attempt and the dishes aren't getting any better. What to try next? I'll try making the clay slab a mite thicker. The customer might not like that as the dish will be heavier, but I can't think of much else to try. The two pieces fit perfectly at the leatherhard stage and seem to be OK at the bisqued stage, but they warp in the glaze firing. Any uneveness in the wall of the piece will cause warping in the final firing, and the shape itself has no built-in integrity. In my flat dishes I make the edges with a little 'wave' to them, and then a slight warp doesn't show. Can't do that here.

Anyway, I mooned around the Studio for a while looking at these things and also the rectangular butter dish I am trying to develop and finally decided maybe it should be a gardening day. After all, it was Sunday.

State of the Week

Yep. Nothing but dumb picky stuff to do in the Studio..... rain, dark clouds, wind, rain..... mosquitoes the size of, well, Smartass..... rain..... can't go out in the garden, too soggy.....mosquitoes like a bad mood.... can't throw new pots, have to get that $#@#@order done.... yellow stain too yellow.... rain.... mosquitoes in the Studio while I'm trying to paint pansies on mugs..... rain....

And it isn't even Friday yet.

Coming Up for Air

That's kind of what I feel like now, like I'm coming up for air! I've worked hard the last couple of months and made lots of pots, including some substantial orders, and now I feel like I can coast for a little while and do some gardening.

The Carp Farmers' Market is open again, the Maple Run Studio Tour is over and went well, I've got pots in a couple of stores for the season..... life is sweet.

Here's a picture of the Maple Syrup Jugs I made for the Tour and the first few weeks of the Market:

The pancakes look pretty good, too, eh!

Then I made some Asparagus dishes and small jugs for the Market opening:

Of course the name is a pun - but I figure you can serve asparagus very nicely on these. You can put the dishes in the oven and warm them before putting the asparagus on, and keep them a bit warmer at the table. Asparagus cools so fast! And of course you need lots of Hollandaise sauce to go with it....

Happy Long Weekend! I hope yours has some asparagus and Hollandaise in it!

Busy Time

A very busy time lately! Surprising, because normally the Winter and Spring are nice peaceful head-down working-in-the-studio seasons.

Did a dinnerware order - several smaller orders - studio tour in March (went well) - Easter Market at the end of March - also went well but quieter than usual - now a rush to get stuff made for the start of the Market season in early May. Add in several group events such as postponed Christmas potlucks, two family birthdays and my local arts society's Mini Conference, and you can see why I'm going to have to hustle to get my income tax done in time. Not that I do it, I have a great retired accountant who does the actual work, but I have to get my records together and organized.

The Mini Conference was something any creative person in the Ottawa area might be interested in. We had some great speakers, a fab lunch, even background music! And of course, lots of discussion. I hate that word 'networking' but I guess that is what you'd call it. Me, I don't 'network'. I 'talk and listen to people'. 'Networking' makes it sound like we are machines and I do not want to be a machine.

I've put a link in the sidebar to the West Carleton Arts Society. The info about next year's Mini-Conf will be up soon and you might want to consider it for next year. A nice boost to your creativity, encouragement, and new friends, can't lose by that.

Speaking of creativity, I'm dreaming up some new projects and I'm wondering what new ideas you might be considering. Anybody want to kick off a discussion by leaving a comment? I'd love to hear your plans!

Clay Tests

It's been a while since I posted.... been busy! One thing that always gets me about doing pottery is how much waiting is involved. Of course I kept busy by interleaving other tasks, but just making some tiles, firing them and then testing them for crazing, etc., seemed to take forever.

First I visited my trusty clay retailer. I was surprised to find that my favourite clay maker* had 5 or 6 white, cone 6, clays available. I had thought there were only 2 or 3. So I got a box of each of the un-grogged ones.

Then I made some 1/2" thick tiles, about 5" square of each clay, including the one I usually use. Then they had to dry. Then I fired them to cone 6, with witness cones right beside them to make sure of the temperature reached. Then I quickly weighed them while they were still warm.

Then I boiled the suckers. Over 2 hours in a huge pot of boiling water.

Then I weighed them all again.

Then I calculated how much moisture each had absorbed, and expressed it in a percentage. (For those who are interested, subtract dry weight from wet, then multiply the result by 100, then divide by the dry weight.)

Shock! Awe!

My 'usual' clay, the one I have been using for years now, had an absorbency of around 2.25%. This was almost the highest of the ones I tested! No wonder I am having trouble with delayed thermal shock. Luckily, one of the others came out to about 0.9 %.

Then I took all the tiles and put them in the freezer overnight and the next day dropped them into boiling water. This was scary, I almost felt like I should 'suit up' in some kind of protective gear, but in actual fact nothing happened.

None of them crazed. Of course, to test for delayed thermal shock, I'm going to have to keep doing it. Since I only like one of the new clays I tested, I'm only going to test it and my 'usual' one. Freezing and boiling every day or so for a month or two should separate the women from the kiddies....

All the glazes worked well with my two production glazes, in fact the clay that had the least absorbency also looks the best with my white glaze. Here's a picture of it with my clear glaze and some brush strokes of the main colours I use. You can see they all work pretty well. BTW, these brush strokes are on top of the unfired glaze, because that is how I work.

Can it really be this easy????


* I put a little 'star' here to explain that I am not going to mention which company's clays I am using. They are a terrific company and I am most grateful to them for keeping us supplied with excellent and dependable clays. They do not claim oven-proof-ness for any of their clays, and they point out (quite correctly) that it is up to us potters to regularly test our products. And no, I do not have any other connection with them than as a customer!