"Fun" With Those F*%&ing Stains

So several years ago while I was developing my "Slate" glaze, I was playing around with some other colours for my matte glaze as well. At the time, I tried a commercial stain called "Blackberry Wine" in my base glaze. I thought it was lovely but not quite what I was looking for at the time.
 

I added a bit of another stain called "Pansy Purple" to push the colour away from burgundy and more towards a dark wine colour. While the colour was exceptional, I lost all of my matte-ness, and shiny was definitely not the look I was after. (The photo doesn't really do the colour any justice, but here it is:)

 As usual, life got in the way and the colour tests got pushed to the back burner. The test tiles went into my huge box with 11 years worth of other test tiles and there it sat collecting dust until recently.

I am still interested in an eggplant coloured matte glaze for my Classic Collection and decided recently to revisit my Blackberry Wine stain. I mixed up a quick sample, based on that very first test as a starting point and was all excited.

Until I opened my kiln.

The colour had all but drained from my glaze and I was left with this rather anemic looking ugly gray. Certainly NOT what I was after.

Now let me explain a wee bit for those not so technically knowledgeable regarding the finer points of glaze chemistry: the stain that I am using to get the original colour uses chrome and tin. These are fickle fiends and require very specific glaze chemistry to pull off their colour magic - no zinc, fire under 1260'C, no magnesium in the glaze and lots of calcium. Check, check, check, and check for the matte glaze that I am currently using.

So what the fuck happened to my colour?!?

An excellent question and one which I have no answer to.

At first I thought maybe I could juggle the calcium in the glaze a bit - perhaps there was TOO MUCH so I bumped it down to the optimal range.

As you can see, the colour got even worse. At least the last time I was getting some speckles of wine colour. This time, nothing but an ugly, flat field of gray.

So I thought I could try adding some other stains to help boost the colour, like that Pansy Purple I tried before:

Or a Deep Crimson:

Better. But not the colour I'm after.

I even tried the Pansy again in a greater concentration:

While it's sorta lovely, there's still too much speckle there for my tastes and the amount of stain required to get this is horrendously high (16%).

So where does that leave me?
I have no flippin' idea.

I am currently at a loss as to why this particular glaze is behaving the way it is, and why it's changing SO FREAKING MUCH from test to test. I'm wondering if there's just too much kaolin in the glaze for the stains to truly come out? Except that I have a stone matte glaze with 5% Blackberry Wine in it and the colour shows up just fine. Or maybe there has been some sort of change to the ingredients that are in the base glaze that I am unaware of? Something coming from a new mine, with slightly different composition? After all, it makes no sense that a glaze that worked fine not three years ago is a complete disaster now. If anyone has any thoughts on this, feel free to post comments. I'm always open to insights.

In the mean time, I'll continue trying to get the colour I'm after. I'm presently trying a new base glaze so we'll see. These things never go as planned, and always seem to take waaaaaaay longer than I'd like. But so it is (sigh).

Yay! Maybe.... Or not?

After last week's post, I tried a bowl without the line decoration.
Let me know what you think!

I trailed a line of my matte glaze all around the rim, and love the way it ran on the inside, and how it blends with the stripes on the outside. I need to work on consistency in terms of applying my darker stripe, and clean up those black pin stripes - I need to get them thinner! I also want to do some fine tuning on the form, beef up the rim a touch, and improve the curve of the bowl. But otherwise, as for the overall shape, I'm pleased.

I'm also anxious to try this with a pale, apple green and a complimentary shade of blue? yellow? orange?. I was trying these early on in this testing series, and I'm almost ready to go back and try again. First, I need to head to the paint department of my local hardware store to stare at paint chips to help me narrow down which oxides to start playing with. But it may be a while before I get the chance to get there.

I'm excited and anxious about these stripes all at the same time. I have to admit, I feel like I'm being pulled in all sorts of opposing directions when it comes to trying all this new stuff with my glazes and my work. It's a little unsettling and even stressful to some extent. It's kinda like heading out somewhere without really knowing where you are going or how to get there, but hoping you make it there regardless.

And I still can't shake this urge to decorate. I wasn't happy with my trailed linework on the previous version of this bowl but I feel like this one is missing something. I'm not sure what exactly that means, and where that needs to go. Part of me just wants to go explore fabric stores, but with my schedule filling up, I can't see finding time for that any time soon. Maybe it's best to push it into my subconscious and let that part of my brain work on it for a while.

And as for all of my testing: you may recall, when I first began writing this little series of posts, I mentioned that I was currently exploring two different directions with my new line of work. These stripes have been one direction. Stay tuned to see where else my creative mind had been going!

A Minor Victory, But Sweet None-the-less

Problems in ceramics tend not to surface until your full-on into production. Case in point: my slate matte glaze.

I love this glaze. I hung onto if for a year, working out how to use it in my work. When my glossy sky-blue glaze struck a chord with the slate matte, it was full steam ahead. Or so I thought. Most pieces were fine. Made it from start to finish with no problems. But anything taller, with straight-ish sides was a whole different ball of wax. I was losing anywhere from 50 to 95% of these pieces in each kiln load.
That's a lot of garbage to be making, and honestly, I can't afford to make trash.

The problem? Large pinholes, or what looks like blisters in the glaze that had popped, the edges healed, but the center remained bare clay. On the smaller of these pieces, like my tall cups, there would be one or two of these blisters. Enough to ruin the piece. Larger pieces, like my large vases, would be covered. COVERED in these blisters. Not a pretty site.

So where to begin?

There's any number of reasons why a glaze would do this, so I just started moving down the checklist trying to figure out what the hell was happening.

Perhaps some organics left in the bisque were causing the problems, but a higher bisque didn't help. Still got blisters.
Moving on, perhaps it was gases swirling in the kiln? I checked my kiln vent, adjusted it accordingly but that didn't seem to help either.

Okay.....

Next thought: water vapour. Thinking wet glazes were casuing problems, I let them dry before loading my kiln.
Nope. that didn't work either.

Okay. Maybe it's from overfiring the glaze? It only seemed to happen on these taller pieces, which also occupy the top shelf of my kiln. Cones indicated my kiln was firing evenly so I tried going from cone 6 down to cone 5. Boy did that ever make the glaze ugly and flat. And the blisters persisted.

With firing things ruled out, I moved on to the glaze recipe iteself. Was there something in there that could be causing this? I sent copies of it off to trusted glaze experts, but they didn't notice anything out of the ordinary. The EPK was a bit high, in the crawling range, but I wasn't experiencing any crawling, and even substituting some calcined kaolin for the some of the epk didn't solve my blister problem.

At this point I was beginning to believe it was an application problem. And I'm not set up for spraying glazes, so that wasn't even an option.

I moved on to glaze additives. First up was some CMC gum. Perhaps the glaze was drying too fast on the ware?
Nope. That didn't help and just made things messy.
Ugh.
Next was some Darvan and sodium silicate. I thought, what the hell, but that didn't work either.

Now it's important to point out that by this time, my husband just cringed whenever it was time for me to open the kiln. It's hard making work when you have orders and deadlines, and you have to throw most of it away. Many kiln openings were accompanied with cursing and/or tears. But I'm stubborn and I persisted.

Chatting with a fellow potter at a show, I asked him if he added anything to his bucket of matte glaze. The answer? Epsom salts. The same epsom salts that ruined my clay body. I tsp per 10kg batch of glaze.
And bloody hell, if it didn't work like a charm!

Epsom Salts, or magnesium sulfate, is a flocculant. These help prevent glazes from settling, which I didn't think my glaze needed since it had so much clay in it. But apparently they also help with glazes used for dipping or pouring. I had come to believe that air bubbles were being trapped against the surface of my bisqued pot when I dipped it, and that they couldn't escape until the glaze was melted. But being a matte, the glaze didn't flow enough to heal the surface like a glossy glaze would. The epsom salts create a porous surface in the raw glaze so perhaps its easier for those air bubbles to escape before the glaze melts?

At any rate, I guess there's a couple of lessons I take away here.
- Don't put out a line of pottery to my wholesale clients until I have worked with it thoroughly first, to try and spot any problems.
-Ask for help. I have no problems with this. Many times I'll get answers that I have already tried, but there's bound to be someone, somewhere, who's done something I haven't thought of.
- and most importantly, never give up! If you want to solve those problems, you have to keep plugging away at them. Now, it's better to do this if you don't have the pressure of HAVING to get things done by a certain date (see the first point) but perserverence pays off!

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!