Gift and Amaco underglaze info at cone 6
Tile by Mary Cay
My good friend and former ceramics instructor, Mary Cay, popped over for a visit last Monday evening. It was so good to see her again and she came bearing a gift for me. She gave me the tile above that I had long coveted and was originally part of an exchange we arranged when I helped her set up her website last year.
It was so good to catch up and I was very excited to hear that she has found space to set up a ceramic studio again in the Denver area after a period of abstinence from clay due to a bit of a life change. I’m looking forward to visiting her studio once she has it set up. Maybe she’ll let me share a few photographs of her studio at a later date….
Bottom of mug attached to kiln shelf
I learned something valuable the other day. I did a couple of glaze tests in my test kiln on a couple of mugs I will be swapping with other EMT members as a part of our annual EMT Secret Mug Swap this month. Unfortunately, this one experienced a bit of a problem and one for which I’m grateful. Why am I grateful, you ask? Because I discovered something about using Amaco LUG Decorating Colors that will save me from making a similar mistake again.
At cone 6, the Amaco LUGs melt like a glaze – they must have some fluxing agents included in the recipe, whereas at cone 05 (the recommended firing temperature), they are a flat matte texture. I figured that if Duncan Cover Coats can fire to up to cone 10 and maintain their color, then the Amaco products should too in theory.
The problem is that the Amaco underglaze acted like a glaze and fused to the kiln shelf – the good news is that it only affected 1 mug and not 40 (the number I have waiting to be glazed this week). Lesson learned. Why does pottery have such a learning curve?
Another good discovery, the raspberry color on the exterior is left over from my cone 6 pink and violet glaze tests and is very stable – it stays put and doesn’t run AND I can brush it on which means that I could conceivably make smaller batches of the glaze so that I don’t have to make big dipping batches.
Meanwhile, I mixing glazes today since I have about 3 bisque loads to glaze in the next week and will visit the Museum of Contemporary Art in Denver later on this afternoon with my family. Stay tuned for more on solar energy in the coming weeks.
Have a good weekend,
~Cynthia
Meredith Heywood
November 1, 2008 at 2:47 pm //
what a sweet tile I bet you could drink that in daily.
Love to have you post the whole mug- I like that raspberry color with the green handle yum!
M
Undaunted
November 1, 2008 at 5:52 pm //
So, is that an underglaze on the bottom of the mug? And that is what melted?
I’ve been reading up on glazes a little since we had our class on it the other week, so I actually understood what you meant about fluxing agents! Just out of interest, which do you think is better: to use underglazes and then a clear glaze on top, or to use coloured glazes? Since it’s not really a proper glaze, can underglazes be used alone?
I’ll have to find out what temperatures the kilns at class are fired at. Sorry, just thinking out loud…
And I agree with Meredith – I love the tile, and I’d love to see the whole mug!
Linda Starr
November 1, 2008 at 8:35 pm //
Mary’s tile is beautiful, I just love her kiln jewels. Looking forward to hearing about Mary’s new studio.
I too love that raspberry color. I am confused on how the bottom of the mug got color on it if the raspberry is stable. Did you underglaze the bottom of the mug?
I used Amaco underglaze on my platters and no runs (not sure which type it was as the bottles are out in the studio right now). I put the underglaze on greenware bowls and platters and then bisque fired to 06. Of course this was on top of the bowls and platters. Then I put a translucent glaze over and high fired (Cone 10). I have my cheese dishes in a high fire load now with a Duncan underglaze I put on them after bisque. I let the underglaze dry and glazed. I hope they don’t run – we shall see. You’ve got me kind of worried now – I took them to another place to get them fired for a show next weekend as the school wasn’t going to get their firing done in time. I know when I was at Duncan’s they advised me that some types of underglazes are for bisque ware and some types are for greenware. I also used stroke and coat (I think Mayco) on some pendants which are in high fire now too, but only glazed the top and they’ll fire flat. I’ll let you know which types of underglazes I used if you want.
wonder if solar can run air conditioning? Our heat isn’t that costly, but our air sure is.
ang
November 1, 2008 at 9:21 pm //
cool lesson learnt, remember note to self!.. your header pic now reminds me of leather, it must be the lighting because it looks concave too..
samir
November 2, 2008 at 2:43 am //
Nice website congratulate for thiswonderful blog.keep rocking.Came to know about it from your mybloglog profile.
Take care,
Sam.
Cynthia
November 2, 2008 at 8:14 am //
Meredith – I hung the tile in a spot in my home where I see it daily
Maybe I’ll try taking a photo of the whole mug later today. My final raspberry color is actually going to be a bit lighter than this one, but it’s still in the same color family. I mixed up a large amount of the base glaze for the raspberry color yesterday so I’m good to go.
Linda U. – Yes – exactly! I guess I wasn’t clear about that in my post – I brushed underglaze on the bottom of the mug for interest and that’s what fused to the kiln shelf. Here’s my thoughts on color and glaze:
I have a couple of glazes that I like and use in quantity such as white, clear, the celadon colored one and I have another called “Chinese blue-green” that I mix up in large batches. I want to add some more colors to my palette and that’s why I’ve been doing so much glaze testing before I commit to making large batches of a glaze I might not like and that would be a waste of money. I made a 10,000 gram batch of glaze and two 5,000 gram batches of glaze yesterday which cost roughly $85.00 USD in raw materials (But, I bought some materials in quantity such as silica, a couple of frits, custer feldspar, epk, om4 and whiting that I’ll be able to use to make more glazes from in the near future.) Some materials are much less expensive when purchased in bulk. Colorants are generally more expensive, so I only buy what I need. I need to look at the glaze calculation software to tell you how much each glaze costs per batch.
Since I’ve been playing around with different colors, it’s more reasonable to use underglazes as a colorant at this point since I might not want to mix up a gigantic batch of a particularly odd color (ie. the chartreuse) – even though ounce for ounce underglaze is more expensive than a homemade glaze. For example, I took a look at a pint of violet Amaco underglaze at Mile Hi Ceramics on Friday and it was almost $24.00! Ouch – that makes the violet glaze (in photo) that I’m making using an Mason Stain as a colorant much more reasonable to make from scratch even though the the colorant is expensive. For example, if I made a 5000 gram batch of violet glaze as shown in the photo, I would need 400 grams of mason stain at 8% – violet is $27.05/pound at Mile Hi Ceramics and since there is almost 454 grams to 1 pound, I would need to purchase a pound of the stain (I’d have a wee bit left over). Given the other ingredients, the glaze would probably end up costing me around $30.00-40.00 for the 5,000 grams which is a significant savings over a measly pint.
A benefit to using underglazes is that they are brushable and you can control exactly where they are placed (good for complicated brushwork) which also serves to eliminate waste. All commercial underglazes are proprietary though – so no recipe if you want to attempt making it in your studio. You can find tons of recipes for engobes and stains to make at home which could replace commercial products – or use homemade slip on greenware for color if you understand which coloring oxides make certain colors. The book I recommended to you, “Spirit of Clay” is one of my favorites and an excellent resource – it has a ton of info on raw materials and oxides that are very readable vs. some ceramic books that are so technical that frankly my eyes glaze over badumdum
It stands to reason that at cone 6 some underglazes act like glazes and could probably be used alone – though I would test. And each color and brand is probably different. If you look back at the link on Duncan Covercoats – some are matte at cone6 and some are glaze like, so it all depends.
Temperature and atmosphere changes everything too – I fire to cone 6 in an electric kiln for my work. I fire my kid’s work to cone 06 in an electric kiln and use a low fire earthenware clay body. The benefit in the latter is that it’s less expensive clay and cost to fire the kiln. Also in the Duncan Cover Coat post, I linked to someone who posted results of firing the underglazes to cone 10 in reduction with different results.
Linda S. – I’m sorry I wasn’t more clear – I brushed underglaze on the bottom of the mug and that’s what melted onto the kiln shelf. You can see from the photo that the raspberry color has a very tight glaze fit and didn’t move at all.
I think you should be fine with your pieces – I just made the mistake of putting the underglaze on the bottom, assuming that it would behave like cone 06 – and I should know better given my Duncan tests! You know what they say about “assuming” anything??
The Duncan Cover Coats are for bisque and the Amaco LUGs can be on greenware or bisque (I think…)
Solar photovoltaic panels can absolutely run air conditioning. When I had the rep over last year, he took into account all of our electricity needs when giving an estimate and determining the size and number of panels to install. My biggest concern was firing my kilns – but here in Denver, we would be still be tied to the grid (no option for going off grid in city limits), so I would have back up if our system failed to produce enough juice so there would be no interruption of power. From what I understand, normally installers put in more panels than is needed and excess power is transferred back to the grid which normally results in receiving a rebate from the power company which is cool. To make it worthwhile, however, the rep told me that we should plan on living in our home for at least 7 years to recoup the financial cost. But, a lot of that equation probably depends on the cost of electricity in your area and the added attractiveness an installed solar system would bring to your home if you were planning on selling <7 years time given the current real estate market.
Ang – I realized that I needed to tweak my banner a bit more, but I’ve been lazy…you’ve given me the nudge to take care of it
Sam – welcome!
Lisa Call
November 2, 2008 at 8:57 am //
Love this tile! And the color of the messed up mug.
Undaunted
November 2, 2008 at 9:18 am //
Wow, so much info! Thank you Cynthia! Yes, the information I had read on glazes was from the book you recommended – as you say, easy to understand and very informative. I feel like I have learnt so much, but I am obviously still a babe! I still haven’t finished the book yet, but I think it will be one that I will read and re-read. I seem to go through “growing spurts” – I take in knowledge, then I have to stop to let that sink in, then I’m ready for some more! Thank you so much for all your support.