Singing the Test Tile Blues

It's that time of year again. Test tiles.

You may recall, I've been working out ideas for a new line of work for quite some time now. This past Christmas things finally came together and I unveiled this new line at my recent wholesale show in Toronto.

Getting it ready for the show, unfortunately, was quite the ordeal. I was struggling to find a nice, clear, durable glaze that I could use with this one that I had been working on a while back. I had a very specific color in mind and set about testing, testing, and testing some more to achieve it. Robin's egg blue. Maybe a bit more of the blue, less of the turquoise, but just to give you an idea. And I had an idea of where to start with my testing. Copper, maybe a fraction of a percent of cobalt to punch it to the blue side...

My guesses were pretty good and in my first batch of test tiles I hit the color I was looking for: 1% copper carbonate plus 0.1% cobalt carbonate. So I set about mixing up a slightly larger batch to get it on some work. It's always easier to get a real feel for a glaze by testing larger batches, rather than just mixing up a huge bucket from what you see on a test tile. Annnnnnd.... I'm glad I did.

Disaster. Super ICK. Bubbles! Everywhere, thousands and thousands of bubbles! My beautiful, clear, glossy glaze was dulled with a pitted surface and microscopic bubbles everywhere. Test tiles are far too small to get an accurate picture of what a glaze will do, and in this case, what the glaze did on a plate, was much different that what it did on a tile.

So. I hit the books. Copper gives off gas after 1975' or so. (Don't quote me on that temperature though, I'm not sure exactly where it starts to get volatile). All that gas was getting trapped in my glaze, even with a hold at peak temperature. Okay. No problem. The carbonate form of copper can release more gas that the oxide form so I mixed up some more tests, using 0.65% copper oxide instead of the carbonate. (The oxide is a stronger colorant). But alas, the bubbles persisted.

Okay. No problem. Tinker with the glaze recipe a bit and I should be able to fix that, right? Working with my Insight program, I tried adding 2% lithium carbonate to the glaze as a way to smooth out the surface. And it worked! But now instead of a beautiful, clear glaze, I had a beautiful, variegated glaze.

Okay. No problem. Back to the Insight program. I removed the lithium and decided to tackle the alumina. I was able to lower the alumina content of my glaze to make it a bit runnier, the idea being that if the glaze flows and moves better, those pesky little bubbles will be able to escape.

Annnnnd, it worked! but now I had yet another problem. Boron clouding. Ugh. The alumina keeps the glaze stiff which prevents boron crystals from forming. Without the alumina, the crystals were able to grow. That means, no clear glaze for me.



With the clock ticking and me needing to resolve this issue, I turned to stains. Yes. Stains. Something I had sworn I would never use. Something I had always considered as a form of cheating. With my head hanging low, I ordered several different shades of what looked like promising colors and went back to mixing up test batches.



The first bunch of tests gave me an idea of how each stain looked. From there, I was able to put together some blends that I thought would push the color to where I wanted it. And as luck would have it, the next batch gave me just what I was looking for.



Actually, it gave me better than what I was looking for. I have a whole new respect for those stains, let me tell ya'. And I may just be turning to them a lot more in the future.

And as for that new line of work...
You may be wondering why it's so different from where my tests began so many months ago. What can I say? There's no telling where creative adventures will take us. I can say, however, that I'm really pleased with how the new line looks!

Testing, Testing, 1,2,3...

Any potter will tell you that testing glazes sucks.
There is just no easy way to do it. It's time consuming and tedious, truly an evil necessity if one is looking for their own glazes that stand out in a crowd.

So I spent many hours this past week doing what I hate: testing glazes.

It has taken me many years to get to a point in glaze testing where I'm no longer rushing through it as fast as I can. I've made WAAAYYY too many mistakes doing just that. I've finally learned to slow down, clear my schedule for the afternoon, pull up a stool and get it done right.

So this time around I'm working on two different glaze bases: a glossy from the geniuses at Digitalfire, and a matte, a recipe that was given to me from the amazing and talented people at NSCAD. I will spend hours researching the colors that I am looking for: what ceramic oxides will yield what results, what ingredients are necessary in the base glaze to give the desired effect. I hunt down appropriate base recipes and calculate them using Insight, a downloadable glaze calculation program (highly recommend it!) and make sure all the numbers look good.

With all the research out of the way, I mix up 500g batches of each, with no colorants, and run each batch through a 120 mesh sieve. Then each glaze is weighed and divided into 5 different containers, all carefully marked with my trusty sharpie. It is at this point that the real test mixing begins. Colorants and stains are carefully measured into each well-labelled container (learned that the hard way, more than once!) and are then ready to be applied to test tiles.

I used to use lots of itsy-bitsy L-shaped tiles that I extruded. Each glazed surface was no more than 1" x 2". I have since moved on to larger surfaces. I found I just couldn't get enough information off of that small a surface. I need to actually SEE what the glaze is going to do, in the manner in which I'm going to be using it. Now I extrude tubes, about 3-4" tall, and 2 1/2" wide. This gives me lots of room to try as much as I need to on the same surface. Each tube is CAREFULLY labelled (also learned that the hard way, more than once!) and at the same time, I make very thorough notes in my sketchbook (again, the hard way...).

Glaze testing is painfully slow. After the research, there's the mixing. After the mixing, there's the firing. After the firing, you have to wait for the kiln to cool. After the kiln cools, you FINALLY get to look at the tiles, and inevitably, try to figure out what to adjust the next time around to get the results you are looking for. It can literally take weeks, months and even years to finally hit the jackpot and get what you were looking for in the first place. As frustrating as it is in the thick of it all, when you finally get that perfect glaze, all of that time spent doesn't seem so bad. It's like hitting pay dirt.

So for all of you out there who are also enduring glaze hell, hang in there! Without all the testing, you'll never find what you're looking for, and sooner or later your efforts will pay off.

More felt, more glaze tests, more frustrations...

Okay. So this has been a rather long and somewhat frustrating week. I managed to get a glaze firing in, along with some of those tests that I am working on. You'll recall from my last post, the problems I was having with my glaze running too much


I mixed up a couple more tests. Both tests are an altered version of the original matte glaze recipe, G1214Z from Digitalfire. I changed the glaze with my Insight Glaze Calculation Program to allow for a 5% increase in Silica. I thought I'd start with this alteration in my tests because it would help to stiffen the glaze and keep if from running, by slightly bumping up its firing temperature. I'm not very happy with the results. The tile on the left has no opacifier, the tile on the right does. You'll notice that I managed to correct the problem of the glaze running too much, but I think I prefer the matter surface of the original glaze recipe. So back to the testing... I think the next round, I'll work on the levels of EPK. If I increase the EPK and the silica at the same time, I may be able to both fix the running, and push the surface more matte. If I simply remove the extra silica and increase the alumina (EPK), then I'll make the glaze more matte than the original, which I don't think is what I want to do. I have to be careful adding too much more EPK, because that can cause the glaze to crawl. Here's an article about this glaze recipe, for further reading.

Back to my felting, I've started decorating some of the tiles I was working on last week:

The small piece on the right is a test piece I tried. The red stripe was wet-felted in place. This creates a very soft and fuzzy line. For the tile on the left, the red lines were added by needle felting. The two colours of wool do not blend the same and the red is much crisper. Personally, I'm leaning towards the look on the right. So I guess I'm testing more of this as well. (I see lots of testing in my future...)

I found some craftspeople online who are willing to answer my questions about felting so now I've got some brains to pick. The RagingWool has offered to help me (I know! Great name!) and so has LaLaFelt who has some amazing roving in stock!

So I'm off for another week of testing: glazes and felting. Enjoy!