Meanwhile, since writing this article about my clay body research, testing and development, I have been planning a series of articles highlighting different materials used in ceramics and with the confluence of the CAD article and these plans, I thought it would be totally appropriate to start “Materials Monday” with Magma (especially since i love alliteration…)
David Pier, the brilliant mind behind MAGMA, approached us shortly before the 2006 Portland NCECA with a demonstration of this new product he had developed. He showed us three water bottles (seen in the image above) containing the same glaze recipe mixed up differently. One had no suspension agent, one used CMC and one used MAGMA. At that time, they had been mixed up for about 6 months. The bottle containing no suspender had settled into a hard mass of all the raw materials and a second layer of just water. NO amount of shaking or agitating would cause the ingredients to recombine. The CMC resulted in a less obvious bilayer result, but, the many of the materials still settled out and had congealed at the bottom of the bottle, The liquid layer was not pure water, some of the lighter chemicals had stayed in suspension, and if you shook it really hard, the agitation clearly would recombine some of the materials, and it suggested that scraping and stirring might offer complete reconstittution. But the final bottle clearly demonstrated the power of MAGMA to keep glazes in suspension. In fact, over ten years later, the glaze containing MAGMA is still in complete suspension.
Very little MAGMA is needed to achieve this stable suspension. Only 3-6 grams per 1000grams of glaze. If you mix up your own glazes, MAGMA is a must. Read more details and buy it here
Well, you CAN make up a MAGMA gel and use it to reconstitute a liquid glaze that has fallen out of suspension. However, if you only use commercial glazes, you might think about just buying the Spectrum Glaze Thinner. I can’t tell you how many times this stuff has truly impressed me with its ability to immediately turn an unusable glaze back to one that looks like it is fresh off the production line. It only takes a drop per couple of ounces, which pretty much means a pint of this stuff will last a lifetime.
So if you’re reading this and thinking “ok, so maybe this stuff is great, but i can just use water too.” Well…..you’re SORT of right. you CAN use water to thin a glaze out, and you can shake it & stir it or you can put it in a blender or use one of those awesome stick blenders or even a Jiffy Mixer, and yes, you might be able to reconstitute a dried out or thick glaze and thin it down so its brushable, BUT here’s what might happen….
- You might add so much water that you end up over taxing the gum in the glaze, causing it to dry so fast while you are trying to brush it on your piece, that it cakes up on your brush, on the side of the pot and just isn’t smooth.
- The next time you go to use it, you might find that the glaze has settled out and you have chunks or globs of glaze floating in murky water. (That probably sounds more dramatic than it actually is, but it’s not good….)
- the pot might come out of the kiln streaky, refractory, or with faded or undeveloped color.
It’s sometimes tricky to know when to use water and when to use an additive. The first thing i consider is if it is likely that water has evaporated from my glaze. If i don’t think the lid was well sealed and/or the glaze is obviously dried out, then i definitely add water (if the glaze is literally a solid chunk, i break it up into small pieces, then add water and let it hydrate for a bit before i start to mix it up. As soon as any chunks feel soft, i will add some glaze thinner, stir to mix throughout, then put on the lid and shake it up. Sometimes it’s necessary and beneficial to let it sit for a bit after doing this (maybe an hour…then check it again…shake & stir and assess if more water or thinner seems appropriate)
Both of these multi-purpose additives come in a 2oz squeeze bottle that makes it easy to measure out a few drops into your glaze. (Bonus- it also helps prevent freezing in casting slip!)
They also make a product dedicated to the many specific glazing needs called Glaze & Color NRG. If you are only using Apt-II for what it does in a glaze, skip the 2oz bottle and go for the more economical pint. This product is formulated to improve the function of any glaze or underglaze. A growing issue i hear about is underglazes popping off during the firing. (most often, this happens when the underglaze has been applied to a dry surface, but sometimes it will happen even when applied on wet clay and dried with the piece. In either situation, Apt-II can help the underglaze to adhere and stay put. It’s also very helpful if you are layering many colors of underglaze (or glaze). You can read more about the features and pick up a pint of this here
For decades, bentonite was the main ingredient added to a glaze recipe to keep it in suspension. (It was also the first ceramic “fact” that i can recall knowing without realizing i knew it….over the years of hearing mom and dad talk apparently some things sunk in without me realizing, and it wasn’t until after my dad was gone and i was working part time at Brackers, helping a customer who had mixed up a glaze that kept settling out. “Did you put bentonite in it?” i asked, surprising myself even as i was saying it. “Dad always said to add 1% bentonite to any glaze recipe whether it is listed or not.” I think my mom overheard from her office and came out to confirm that i was right.). Even with so many other magical mystery ingredients, bentonite is still a dependable, reliable and inexpensive suspension agent for glazes. There are lots of different versions of bentonite, (Bentolite L-10, HPM20, VeeGum-T, Macaloid, and so on) but unless a recipe calls for one of those specific types, regular old bentonite will do nicely
CMC (Carboxy Methyl Cellulose) is a powdered gum that can be added to a glaze to act as a suspending agent for dipping glazes. Mostly, it is used as a hardener, however. It reduces shrinkage of a glaze and thus reduces cracking when drying. CMC can be blended dry with your other glaze ingredients and then mixed with water. CMC cannot be added to a liquid glaze while still a powder. It must first be dissolved in boiling water and then blended with a high speed immersion blender. As it cools, it will thin out. (And really, even if you are mixing glazes from dry ingredients, adding the CMC gum as a liquid after the fact is often preferred). You can also use a commercially available, pre-mixed gum solution (see next tab)
One of the most helpful analogies i have heard regarding CMC is to think of it as a glue, that helps stick your glaze to your work until the firing is complete.
Gum solution is an ingredient in most commercially produced liquid glazes, that aids in brushability, suspension, and glaze adherence to the piece. It slows the drying time and prevents a variety of glaze application mishaps. Gum solution CAN break down over time, (or if frozen) which reduces or negates the effectiveness of the gum, so occassionally, you might have to add more.
Conveniently, just this morning, AMACO posted an article about gum solution:
Gum solution can be used to thin overly thick glazes, and bring them back to a brushable consistency, and to prevent glazes from cracking as they dry, which can lead to crawling on firing. AMACO Lab recommends using no more than 1/4 cup of distilled water to each Tablespoon of gum solution. Using distilled water instead of tap water will lengthen the effective time of the gum solution. Add the gum solution in small amounts, along with water, to thin glazes which are too thick. Add gum solution alone to glazes which are old, smell bad, or are cracking as they dry.
VeeGum is actually not a gum. It is a smectite clay mined and refined by R.T. Vanderbilt. It is most often used in clay bodies as a plasticizing agent, but in a glaze, it functions much like a gum, acting as a surface hardener. In some cases, it can even be sprayed on the surface of a piece prior to glazing. This is often useful when doing delicate brushwork.
Also like gum, it must be first hydrated before adding it to a glaze or using it to apply to the surface. It takes a lot of time and will create a slurry.
Sometimes, VeeGum and CMC Gum are combined (available as VeeGum-CER), which is reported to provde optimal hardening, suspension & viscosity stablization.
In case you can’t make out her handwriting, the card reads
“Additive for glazes that don’t stay in suspension
Mix Epson salts and HOT water to a super saturated solution..
Add at least 2 tsp solution to 1 gallon glaze.”
Also, it’s apparently “really old”
My dad always had Glycerine in the house when i was a kid. To me, it was the magical ingredient he would add to bubble solution to make the bubbles bigger, stronger, and longer lasting (by increasing the surface tension). In glazes, it increases brushability. It can also be mixed with mason stains to create a mixture that will work well with rubber stamps. It is readily available at pharmacies or craft & hobby stores like Michaels or Hobby Lobby (it is used in soap making, so you can get it in bulk, quite useful if you have kids who like having fun with bubble wands)
If you’re still with me reading this lengthy article on the first Materials Monday, and you still want to learn more, here are some of my references and suggestions for further reading:
- Pete Pinnell’s article from the May/June 1998 Clay Times on Adjusting Glazes
- DigitalFire Database
- The Ceramic Arts Daily Article
- AMACO’s Gum Solution Article
- Potter’s Dictionary by Frank & Janet Hamer
- Potter’s Complete Book of Clay & Glazes by James Chappell
- Mom’s index card file/bulletin board notes
Be on the lookout for the next Maaterials Monday post, *probably* coming out in a couple of weeks. maybe three…we’ll see. It’s important to me that what i post is well-researched and accurate, and that takes time.
On that note, if you read something that you don’t think is accurate, let me know and i’ll do further research and revise as necessary.
I have a long list of topics already, but if there’s something you want to know more about, Materials monday suggestion