Red Hot Reds: All You Need to Know to Make Beautiful Red Glazes

In today’s post, David Gamble discusses a red hot topic for many a ceramic artist: how to achieve reliable red glazes. If you have ever tried to formulate a red glaze, you know how difficult it can be. And even if you buy commercial red glazes, you understand that they need a certain amount of attention and precision paid to them during application and firing.

This article will help you understand and keep track of all the variables when applying and firing red ceramic glazes. – Jennifer Harnetty, editor.


 

Untitled, by Scott Bennett. Amaco LM series Coral glaze with wax and Black overspray. As the wax melts in the kiln, the black moves.

I’ll start by explaining there are two different types of commercial red glazes that I normally use. One type is an extremely bright color and harder to achieve and the other is a newer tomato red color that is AP (Approved Product of the Arts and Creative Materials Institute) nontoxic and dinnerware safe. The latter is  formulated with inclusion stains, which are continuing to be improved. The color is encased in zircon, which makes them safe to use even in the classroom.

The AP nontoxic reds are extremely stable and were used to create red velvet underglazes that can be fired from cone 05 to as high as cone 10 – only salt seems to blush them out.

The success of underglazes has allowed the development of gloss and matt red glazes that have been formulated to work well at the low-fire cone 05 range and other glazes formulated for the cone 4-6 range. These are extremely reliable. Three brushed coats will usually be enough of an application and you get nice tomato color reds at both temperatures.

Bright reds are not dinnerware safe and are extremely sensitive to variations in firing conditions. There have been many times that an art teacher has asked me about the use of these types of red glazes. I understand the space and time challenges that teachers face, but you cannot put these glazes in with your normal glaze firings and expect good results. They are affected by how tight the load is stacked, other glazes (mostly copper greens), and temperature. If you’re firing to cone 05, I can almost guarantee there will be problems. The glaze will most likely have variations from clear to gray to black, and if you’re lucky, a spot or two of red.

Note: Amaco glazes were used in the pieces shown here, however, many companies produce similar glazes.

Process

Here are my suggestions of what you need to know and do to achieve the bright reds!

Plate, by David Gamble. Cross is glazed with red underglaze.

Bisque your clay body slowly to cone 04 (12 hours to get all the gases out). Although these glazes are not considered translucent, the clay body color does affect them slightly. White bodies will make the glaze appear brighter in color than darker bodies.

Using a brush, apply the glaze thicker than the normal three coats. Four coats will usually work, but too heavy an application may cause the glaze to run. Glaze application may need experimentation and practice.

Load the kiln very loosely. There is a need for lots of space between the pieces for air circulation. I leave the peephole plugs out during the firing, thus allowing extra oxygen to enter the kiln chamber.

Do not fire above cone 06 (1828°F), preferably using witness cones for observation. I have been firing at cone 07 (1789°F) with great results. These glazes seem to like the cooler temperatures.

Fire as quickly as you can, four hours is ideal. If your pieces are larger, an example being my 22-inch platters, take them up slowly to about 1200°F. This may help to eliminate cracking problems. Then turn the kiln on high to fast fire to the end of the firing.


More Observations

“Redhot Chilli Pepper Diner,” by Jerry Berta. Glazed with red underglazes.

If your kiln is vented through the bottom with a system that draws air through the top of the kiln, this will help give you more oxygen in the kiln and better red results. Remember that kilns, depending on how they are stacked, may not fire that evenly. This can cause cold spots and hot spots. There can be a difference in temperature equal to a couple of cones from top to bottom-depending where the kiln sitter or thermocouple is located. This variability can really affect bright red glazes. Newer kilns with zone control and multiple thermocouples tend to fire more evenly. If you have an older kiln, place cones in the top, middle and bottom of the kiln so you can keep a record of what happens in the firing. They can help provide answers if problems do occur.

Now that you know the process, I will describe my experimentation with red glazes. I’ve been placing them on different color clay bodies, layering over glazed fired pieces and layering one coat of gold glaze over the top.

I then place the pieces next to peep holes to brighten the color or place shelves over the edges to deepen and take away the color. This is what is exciting to me – not getting it perfect, but having the surface color change and vary while having some control over what the changes will be. I am an extreme advocate of using commercial glazes the way a painter would use his tubes of paint. Experiment, test to the “max” and make them your own. Years ago, I was asked to be a glaze doctor at the National Council on Education for the Ceramic Arts (NCECA) in Las Vegas. I agreed, but told them to label me a glaze deviate instead of a glaze doctor.

Don’t be afraid to experiment. Don’t be afraid to sacrifice a few pieces on the way to discovering something more exciting.

 

Comments
  • Vilya T.

    I am still waiting on a good recipe for making a red glaze….not sure I got it from the above. I already use bottle/commercial red glazes…firing with gas.

  • David,
    I am curious because you wrote that bright reds are not dinnerware safe. We eat our meals upon Watson’s copper-red recipe (CM Summer 1985). I fired my dinnerware ^10 reduction.
    Do you have a tombstone suggestion for us or perhaps a red glaze which is food safe for ^10 reduction?

  • Hawkowl (.

    Interesting, I wonder about Walter Dexter’s famous reds and I see in Hesselbeth and Roy’s Mastering Cone Six glazes that they have a raspberry red that looks lovely but I haven’t tried it. Any Comment?

  • Amy P.

    I’ve never had any trouble with Spectrum’s cone 6 red glazes, and they are all labeled as food safe.

  • Viktor G.

    Quite good glazes. But the best low-fite tomato red is real uranium-red lead glazes. For example You can try a simple, but beautiful composition: 61.5 % red lead (minium), 16.2 % quartz, 7.7 % kaolin and 15.2 % uranium oxide. Fire to cone 08a – 07a (940 – 960 °C) in oxidation 🙂

  • Viktor G.

    Quite good glazes. But the best low-fite tomato red is real uranium-red lead glazes. For example You can try a simple, but beautiful composition: 61.5 % red lead (minium), 16.2 % quartz, 7.7 % kaolin and 15.2 % uranium oxide. Fire to cone 08a – 07a (940 – 960 °C) in oxidation 🙂

  • Erin T.

    Mastering cone 6 glazes – the raspberry is NICE.

  • CHRIS G.

    my main glazes are very good copper reds 4% tin with 1/2% copper carb reduced from about 800o C, very safe for food.fired to cone 10-11
    the other is a tomato red about 10% red iron oxide for to cone 8 in oxidation again food safe.

  • Robert W.

    @ nancy ache, if you need a good red at cone 10 reduction, we use Laguna chun base and add 0.5% copper carb. It works great for us and is food safe and all that jazz. We dip our glazes so the application is on the thicker side (never brush on) Although reduction is a huge factor, if reduced properly you get a great rich red (i reduce at 1840 until done) but if it’s pink, flat, or burns away, you have to adjust your reduction. hope this helps 😀

  • Daniel H.

    This article is about electric firing. Fuel fired kilns can achieve food safe bright reds in reduction. I get dependable copper reds at cone 10 with 1/2 percent copper oxide. If you add 1/2 percent triple fine (XXX)silicon carbide to your glaze you can cut the reduction time down to about 15 minutes near the end of the firing.

    D. Heinecke

  • Chantal G.

    I agree with Vilya Thomas, i’m also looking for a good cone 6 red glaze recipe. Has anyone ever tried the ketchup red recipe ? I’ve tried it but with very bad results.. 🙂

  • Thanks Rob, my copper is .3% with 1.0% tin oxide. I usually begin reduction about 1600, and get some white pots in not so sweet spots of the kiln. Do you think if I increase my copper carb. to .5 I’ll have better reduction?

  • Subscriber T.

    Nancy,
    I believe there is some confusion on red glazes.

    Cone 10 copper reds are food safe. they have no lead in them.

    Cone 6 chrome /tin (raspberry) reds are food safe

    Cone 06 & cone 6 inclusion stains are encapsulated colors and are generally safe

    Cone 06 lead/chrome reds are not food safe and should not be used.

    The second part about copper reds in reduction is that improper reduction will cause a great vibrant copper red to go muddy. If you have a beautiful copper red you have proper reduction. The white streaks are where oxygen has killed the reduction and the copper red, so only partial reduction is taking place in the kiln.
    Hope this helps.
    Wyndham

  • Alison

    Hi I’m firing earthenware 1060 / 1100C reduction lustre glazes using copper carbonate & or silver carbonate in a lead frit/ alkali glaze in an electric lustre kiln. I have just set up a small gas kiln and want to do the reduction at 680-700 C.
    I’ve been told by another lustre potter that its difficult to get a reducing atmosphere at that low a temperature & I need a gas analyser, so my question is what analyser do you recommend and there any one out there who is into this alchemy?

    Bridge Pottery Collective

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