In ceramics, zero DOES have value!

This blog post is intended for anyone new to the field of ceramics and pottery - it's just a quick explanation of how to interpret cone-speak. 

When I first got into pottery, I have to admit that a very specific (yet very important!) corner of pottery jargon tripped me up -- the use of the word 'cone' to describe heat accumulation. I seem to recall thinking that saying you fired a kiln to cone 6 was kind of like asking someone the time and having them tell you 'banana'. Until I understood cone calibration, there was just a total disconnect between the words and the meaning.

So why the blog post? To reiterate a very important point that is VERY important to those new to ceramics to grasp -- that Cone 06 and Cone 6 are NOT the same thing.  See that '0'? That makes all the difference, and this blog post explains why.

In the first place, a cone is exactly what it sounds like - a small, cone-shaped object that is made from ceramic materials that have been formulated to melt or slump at a particular accumulation of heat -- here, heat being the interaction of temperature and time. These cones have been assigned standardized numbers that correspond to a particular accumulation of heat. 

Self-supporting cones, sold in boxes of 50.

These cones bend when they melt, which tells you - the person firing the kiln - just how hot the kiln is inside. Cone 06 (say it like 'cone oh six) melts at 1830 degrees F when fired at a rate of 150 degrees per hour, where cone 6 (say it 'cone six') melts at a higher temperature - 2232 degrees F - when fired at the same rate. So, there IS a significant difference as indicated by the inclusion of that '0'.

 

The slumped cone of the left is a Cone 08, which melts at a lower point than 

Cone 06 (center) and Cone 8 (right) 

So that all makes sense, right? Basic concept, basic explanation -- so why dedicate a whole blog post to this? Well, one funny thing about the commercial ceramic industry is the fact that many clays and glazes tend to be formulated for two very popular firing ranges -- Cone 06, and Cone 6. 

For anyone who works in the low-fire clay and/or glaze range, that roughly translates to Cone 06. Popular low-fire glaze lines, like Mayco Stroke & Coats, Duncan's Pure Brilliance clear glazes, and Amaco's Liquid Gloss series are all formulated to be fired around Cone 06. 

Another very popular firing range is mid-range, or right around Cone 6. Amaco's Potter's Choice line, for example, is a pretty well-known mid-range line. 

So while it's just sort of an interesting coincidence that the two cone ranges that happen to be standards within the industry sound an awful lot alike, it does need to be mentioned again that 'Cone 06' and 'Cone 6' are NOT interchangable! If you fire a low-fire (or, say, something in the Cone 06 range) clay or glaze at a mid-range (Cone 6) temperature, you run the risk of drastically OVER-firing (and likely ruining) your work. You'll see low-fire clays slump and melt when too much heat is applied; low-fire glazes can run right off of your piece and even wreck your kiln shelving!

Check out the image above, taken from Joe Kowalczyk's Adventures in Kiln Repair blog. That disgusting mass you see up there is actually over-fired clay -- yep, that's what can happen when you muddle '06' and '6'. Yikes!

Mixing up the cones in the opposite direction is not typically quite so destructive, but you can still end up with a lot of weird-looking pottery. When you fire a mid-range glaze intended for Cone 6 at a much lower temperature, like Cone 06, you UNDER-fire your pots. This can result in chalky, un-vitrified surfaces that are often just not very attractive.

This example of underfired work comes from the blog Paul the Potter. See how the surfaces are dull and chalky? Because the kiln didn't get hot enough to melt the glassy elements in the glaze that would form a slick, gloss surface, the end result just looks kind of unfinished. Classic underfiring -- and pretty much what you might expect when you place a Cone 6 glaze in a Cone 06 firing (although, it should be noted, the image above was the result of a much more nebulous firing issue). Of course, with under-fired work, you can always just re-fire it at the proper range, but it's still a net loss of time and energy.

So! In conclusion, know your firing ranges for the clays and glazes you use. Know that the small '0' you see on glaze instructions should definitely not be ignored! Know there is a difference between the low-range Cone 06 and the mid-range Cone 6. I'll leave you with a handy, techy-looking firing chart, so this post looks even more official:

Same glaze, different clays

Because we're always trying to improve the products that we make here at The Ceramic Shop, we tend to do a lot of testing. Whether we're developing the perfect wax products or finessing our glaze offerings, the more we know about our our items, the more information we can pass on to you.

One question that we get VERY frequently is a very general inquiry: 'Why doesn't the glaze on my piece look like the tile/chip/picture?' This is a question that spans glaze firing temperatures, brands, application methods...name the variable, and it has come up when we field this question.  However, in many cases, the answer is quite direct -- the base upon which you put your glaze (whether you dip, paint, or spray) will have a major effect on how your glaze turns out.

To demonstrate just how intensely your claybody can affect your final  glaze outcome, we've tested our Cone 6 Professional glaze line on four different claybodies that represent a good swath of the claybody color spectrum. We narrowed down our testing on the following claybodies:

1. Standard 365, a cone 6 grolleg porcelain.

2. Standard 240, a white cone 6 stoneware -- as white stonewares do not tend to be as crisp and bright as porcelains, we thought it would be good to show them side-by-side.

3. Standard 259, a buff  cone 4-10 stoneware -- this is a stoneware that can actually get pretty toasty in reduction, but in oxidation it remains a mid-toned tan/brown color -- and a great deal of stonewares will fall into this general color range. 

4. Standard 266, a dark brown cone 4-6 stoneware.  This is definitely on the darker end of the claybody color spectrum -- and that color is delivered by various oxides that exist in the claybody. I mention this as you peruse through our results because you will notice that the examples of glazes on this claybody in particular feature some pretty drastic results -- that is a direct result of all of the 'stuff' (er....oxides and colorants) that are in this clay, and impart their qualities to objects that come into direct chemical contact with them, such as a glaze coat.

  

OK!  So, onward with our test results...

Here's a good starting point -- a side-by-side comparison of all four claybodies dipped in our Classic Clear..  

This is a clear, glossy coating that really allows the underlying claybody to show through. Fairly predictable results -- basically, a layer of clear glass has been melted over the surface of these clays, allowing their natural colors to shine through. 

If you add a bit of colorant materials or opacifiers to a clear glaze, you get a translucent glaze - and here at The Ceramic Shop, we carry plenty of these. Translucent glazes are kind of like the tinted windows of the glaze world - they cast a definite tone upon the clay that they are placed on, but that clay still shines through a bit, as well.  We have had customers who are rather surprised by just how much the underlying claybody can, indeed, affect a strongly-colored, yet translucent, glaze.  Here's an example, with our Cotton Candy:

Here, some visualization can help - say you are tasked with re-painting a room with very dark walls. If you are painting that room a significantly brighter color, you might really need a primer if you want you new shade to display its full brightness. To this end, I often suggest to people who work with darker claybodies to consider using a light-colored or white slip over the areas they might like to glaze in a bright color. And, sure, this sort of analogy makes sense when you think about the nature of translucent glazes. 

However, we also frequently have clients express their surprise at just how significantly claybody color affects opaque glazes. These are glazes that are completely solid and do not allow light to pass through; as such, it makes sense that you might think of them as less influenced by the color of the surface that they cover, right? The thing is, though, many reactions you see in a glaze surface are distinct chemical reactions that rely on the interaction of different materials -- and, for color response, this often means oxides. Red iron oxide, for example, is a very common -- and very powerful! -- material that can be found in many, many different clays and glazes. The dark stoneware that we used for these tests very likely contains this, for instance. 

When a glazed vessel goes through the firing process, it's not simply a matter of the glaze becoming fused to the clay's surface. A very small zone of mixing actually happens, where the interface between the two is a clay-glaze hybrid. This means that any oxides that the claybody might contain can indeed actually become physically enmeshed into the glaze -- and that, in turn, can alter the end-result color, even when the glaze is opaque. Here's an example with our very popular Tidal Pool glaze:

As you can see, this opaque blue-green glaze looks pretty much the same on whiter and lighter clays - but it looks completely different on the dark stoneware. The colorants that form the green/blue tones in the glaze have clearly been overpowered by the coloring oxides in the dark stoneware's claybody, resulting in a brown -- NOT green -- glaze. While we expected a degree of variation, this was one of those tests where the outcome was actually a bit more drastic than we thought it would be, which just goes to show the importance of testing your glazes whenever possible!

For a final example, I want to demonstrate just how much an underlying claybody can affect the look of an opaque, but lighter-colored, glaze. Most studios are outfitted with some sort of an opaque white glaze, and this tends to be a look that I use as my go-to. Here at The Ceramic Shop, we have a White Gloss and a White Matte, and both are unsurprisingly popular. Below, though, check out just how much a darker claybody can affect an opaque white glaze:

The first three examples are fairly predictable, but it's clear that the dark stoneware delivers significant effect to this particular glaze. For the record, these tiles were all fired in the same firing and photographed in the same light. I mention this because the change in the white matte when applied to a darker claybody is, indeed, remarkable. 

If you use or are thinking about using our Cone 6 professional glazes, you'll be happy to know we have been working hard to compile user resources on our website -- and we have many more tile comparison charts, featuring your favorite Ceramic Shop glazes. We will be adding to this until it's done! You can check out our application and firing suggestions here.

If you have used The Ceramic Shop's Cone 6 Professional Glazes and have some tips, tricks, or results you would like to share, we'd love to hear from you! We welcome comments here on the blog and we love to post customer work on our Facebook page.

Small 120-volt kilns for small spaces

We offer a firing service to those in the Philadelphia area, and one of our more popular models is our tiny ConeArt BX119 kiln. While plenty of people rent out the kiln for glaze tests, most are actually working on smaller-scale objects, primarily jewelry and buttons.  We've even seen a few customers over the years wind up purchasing their own test kiln, because these are usually built in a size that is manageable for a smaller space, such as an apartment, AND -- total bonus -- they are typically wired for 120v, which means they can be plugged in to your standard household outlet. Because we've noticed that people have been surprised to hear this, here is a rundown of our smaller kilns that could make a great addition to your home studio, especially if you are working on a small scale.

Below, I've broken down our small-scale kiln offerings into three categories: mid- and high-fire (kilns that reach cone 6 or cone 10); glass-specific (many of which come equipped with digital controllers with glass-specific programs); and mixed media, which are suggested for glass, some low-fire clays, and metal clays such as PMC (which are typically VERY low-temperature). Why the distinction?  Although there are SO many options out there for smaller 120v kilns, they aren't all built with the same purposes. As always, before you buy a kiln, make sure you know what you'll be using it for -- kilns designed to handle lower-fire materials such as glass and PMC aren't always capable of transitioning to the higher temperatures that, say, porcelain requires. Just something to keep in mind! Without further ado...

HIGH-FIRE

Smaller clay projects, including clay jewelry, can be fired in the kilns listed below.  They are capable of bringing your work to both bisque- and glaze-temperatures, which means they all reach the cone 6-10 range. 

Our newest small kiln offering is the Paragon Happy Clam. This is a clam shell kiln that has an interior space of 8"x8"x6.5". A clam shell kiln is exactly what it sounds like -- instead of having  door on the front or top of the kiln that you open to load, this style is basically a shell that fits over a floor with a hinge.  

Happy as a clam

The benefit of a clam shell model is in the loading. If you find yourself making delicate, tenuous work (as many glass and jewelry makers do), you may find it difficult or tedious to load a kiln stack -- even a tiny one! -- from the top or the side.  With a clam shell kiln, you build your stack in such a way that it's accessible from 3 out of 4 sides, ensuring that you can build the perfect load.  Then, you simply lower the body of the small kiln over your work. 

With a digital controller and a cone-10 firing capacity, the ConeArt BX119 is a powerful, yet easy-to-use test-sized 6-sided kiln.

ConeArt BX119

As I mentioned in the intro, this is one of the kilns that we use (on a near-daily basis!) as part of our in-house firing service; having personally done many glaze tests in this specific kiln, I've long been a fan of its quick, reliable firings and easy-to-use 12-key controller (that comes pre-programmed with both bisque and glaze programs). Of course, you also have the option to write and store your own firing programs in the kiln's computer, and although it's compact, it's still a great shape for accommodating smaller work. I can fit 4-5 mugs per firing, and the space is actually large enough to accommodate our large bead rack - so that's a great tip for you porcelain jewelers out there!

Finally, the Olympic Doll/Test kiln is a great option for anyone looking for a relatively affordable, energy-efficient kiln. 

Dollbaby!

You can select your preferred features on this kiln -- it can be built to be manual, or can come equipped with a 3- or 12-key digital controller. Likewise, when you buy an Olympic kiln, you can know that you've made an energy-efficient choice. While all kilns strive to contain heat as well as possible, this has become a cornerstone of Olympic's selling points. Their kilns tend to have thicker bricks, and therefore, they hold in more heat. This can be a really nice feature when it's summertime and you're firing your kiln...inside your house.

GLASS KILNS

What makes a small glass kiln stand apart from kilns designed to handle ceramics?  A few things, really. In the first place, glass kilns tend to have an element placed in the kiln's lid to ensure even heat coming down from the top of the kiln.  Because even a small differential in heat distribution can result in cracked glasswares, this element serves as a very important safeguard -- and while you might see such an element in SOME kilns intended for firing ceramics, it's certainly rare. 

EvenHeat GT-14-6

The nice thing about this EvenHeat Studio Pro 14 is the fact that is does have a full 14" x 14" space for all of your in-home glass projects. 

We find this size is definitely on the larger end of 120-volt kilns; its clam shell model will be helpful when loading delicate work, and the ceiling element ensures even, top-down heating. this particular kiln comes with a very easy-to-use 3-key controller that has pre-set programs specifically designed for glass slumping and fusing.

For the glass or jewelry artist who is primarily looking for an annealing kiln, the EvenHeat Fishbone is a straightforward choice.

EvenHeat Fishbone

Specifically, this is a kiln designed for glass beadwork, so if that is your chosen media, look no further! 

MIXED MEDIA

Mixed media kilns are great for artists who tend to use a lot of materials -- glass, enamel, and PMC (metal clay) are the most common mixed media that are used in these kilns, although certain models can indeed do both glass and low-fire clay.  With smaller-model kilns, it's not too common to see them designed to handle both glasswork AND higher-firing ceramics, so please keep that in mind as you shop mixed media, and read the firing capacities carefully.  As always, call us or email us fi you have any questions!

For the fashionable small-object maker working in glass slumping/fusing, enameling, or metal clay (PMC), the Evenheat Kingpin 88 is popular because it comes in a wide variety of colors. This means you can literally match your kiln to your decor!

EvenHeat Kingpin. The fashionable kiln choice.

A great all-around kiln for mixed media is the Paragon Caldera. This is a very popular mixed-media kiln that actually CAN do it all -- from PMC to glass to, yes, even high-fire porcelain!

Paragon Caldera

This kiln is multi-use, fits into your home, and can pretty much fire anything you throw at it. Plus, it's very affordable. This kiln also comes with a few customization options - you can opt to add a bead window, or a collar, which increases the capacity of your kiln. 

So that's it for our general overview of smaller kilns -- we actually have many, many more on our site, so hopefully this primer will help you get started as you look for the perfect piece of equipment for your space. If you have any questions, we're happy to answer them -- call us at 215-427-9665.