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Mid-Fire Glazing 101

For me, each time I enter a clay studio it feels like going to the candy store. When I was a kid, after getting my allowance I couldn’t wait to go shopping at Ben Franklin.  They had an entire aisle for just candy! It was incredible. Perhaps, now, it’s fairly common to see an entire aisle of candy, but back then this was unique to Ben Franklin and it seemed magical to me. My big decision was always choosing between one chocolate Hershey bar or a bag filled with penny candy. The chocolate bar would be amazing but gone before I got home.  The candies were yummy and would last for days but they were not chocolate.  Some weeks I chose a Hershey’s bar, others I chose the candies.  The combination of flavors, smells, and textures were always wonderful no matter what I picked.

A clay studio also presents a long list of exciting possibilities. The number of possible clays, shapes, textures and glazes are endless.  Finding the sweet spots, where the four work together, is what I love about working with clay.   The choices and combinations can interact in complicated, and not always clear, ways.  For example, while picking a clay body, I need to consider the effects on the other steps when making my decision.  If I want to build a large structure, then I’ll need a clay that has enough grit to support the structure.  If I’m interested in smooth surfaces and intricate details, then I’ll need more of a white stoneware or porcelain.  I also need to consider how the clay body I pick will affect the textures and glazes. If I choose a gritty clay, then the textures will be more rugged.  If I want a fluid texture, then a clay with less grit would be a better choice. I also need to consider the color of the clay.  A bright yellow glaze applied to a red clay may result in an earthy brown when the iron in the clay blends into the glaze.   Lots of choices, lots of fun - penny candy and Hershey bars all over again.

In order to gain some direction, and to avoid being too scattered, I prefer to keep the clay and shapes fairly limited.  This allows me to explore the interactions between textures and glazes while also maintaining some sort of signature look to my work.

Before I can fully partake in this dance of textures and glazes, I must build an understanding of the glazes that are currently available to me. I need to know how fluid the glazes will become in the kiln. Will the brush marks or drips show after the firing or will they blend in?  How will the glazes interact with other glazes, slips, or oxides?  Will the final color be transparent, opaque, or cloudy?  Will the surface be glossy, satin, or matte?  Will these glazes enhance or cover the textures?  Once I get this knowledge then I can begin to create a successful, coherent body of work.

To start this process, I had to go shopping.  Shucks.  The Internet makes this far too easy and, of course, I was a bit overzealous when purchasing glazes.  Out of tradition, I grabbed some earth tone browns, yellows, and reds. I also had a bias that mid-fire electric glazes should be bright primary colors so into my basket I put reds, yellows, blues, and greens. I was going to embrace this new-to-me style of firing.

Initially the only information I had about the glazes I purchased, was the jpeg images available online.  With not much to go on, I viewed my first several firings as initial experiments to build a base. I needed to be playful, record everything, and identify which interactions were interesting.  I needed to start building my working knowledge of the glazes.

Time to Glaze

As I was getting setup to start glazing (on my kitchen table), my four-year-old daughter became very curious about what I was doing.  She really wanted to help.  Why not!!!   She picked out a mug, grabbed ALL my brushes, and confidently started glazing just like Mommy.  I was amazed to see how much she had learned.  She glazed the inside, used a separate brush for each glaze, and she didn’t stop until the entire mug was covered with glaze.  She looked so proud to be helping.

After her bedtime, I finished glazing the remaining pots, carefully packed them into boxes, and took them back to the studio for the final firing.  About a week later, I got a message from Carey that my pots had been fired!  I grabbed a cardboard box, a bunch of towels, and drove to the studio excited to see our final results.  My reaction to seeing pots after a firing is always a whirlwind of emotions.  I quickly judge the pieces as working or not working.  Like all first impressions, my quick judgements are often wrong and miss many wonderful subtleties.  After a couple of days, I can start looking at the pieces with a more sophisticated eye and start building my knowledge of how the glazes respond to different situations.  Most important, I start recording my goals for each piece, any lessons learned, whatever I find interesting about the piece, and ideas I have for future work.

Journal Entries

Laney’s Coffee Mug

I’ll start with Laney’s mug.  When I made this mug, my intention was to try out the Amaco Shino glaze.  Shino is a traditional glaze that at cone 9-10 works nicely with throwing lines and has a nice semi-glossy surface. I was curious if the mid-fire Shino would have the same depth and beauty.  Yet, when Laney claimed this piece as hers, I knew the glaze was no longer my decision.  I suggested the Shino and her response was “ick”. Instead, she picked the bright colors of Coyote Baby Blue and Coyote Buttercup.

Of all the pieces I had in that first firing, this mug gave the most information.  I was able to learn about the surface areas, response to slight variation in temperatures, transparency, and the stability of these glazes.  Funny how the more you play the more you learn.

For the surface areas, I noted how the yellow glaze has a glossy finish that is nice to touch while the blue has an uncomfortable dry and pasty surface. On the inside of the mug, the blue glaze does have a slightly glossier finish. It is still matte but much more pleasing to touch.  During the firing, the glazes often reach a higher temperature inside the pieces due to heat trapping.  I now know that when using the blue glaze, I need to reach a higher temperature if I want a satin surface.

Glossy and matte surfaces are both acceptable but knowing this aspect of the glazes changes where I’ll use them on future pieces.  For instance, a matte glaze on the inside of a bowl where you’ll be dragging a spoon to get the last morsel of pesto won’t be very pleasing.  Think of the “finger nails on a chalkboard” sound.  Yet, a dry surface on the outside of a mug on a cold day may help you feel a little cozier and a bit warmer.

I also learned these two glazes do not move when fired.  On this one mug, Laney was able to include glaze drips, overlapping of the glazes, and a variety of thickness of both glazes. Every brush mark and glaze drip is still visible. On future pieces, I’ll need to use a pouring/dipping method or use only purposeful brush marks since the surface I create when using these glazes will be the final surface.

Even though both glazes are rather opaque, when one is applied over the other, both are visible and they don’t blend together.  Instead, the overlapping creates a spotted result. In the places where she brushed a thick layer of yellow glaze over the blue, prominent blue dots poked through the yellow glaze (Figure 1).  Whereas when she put a thin layer of yellow over the blue then the blue dots are there but more faint and the texture is somewhat like a broken butter sauce (Figure 2). The glazes did not mix, instead the color underneath pushed through the top color.

Wow, that is a lot of information from one little mug! The best part of getting this mug back from the firing was seeing how proud Laney was with her piece and how excited she was to have her own coffee (cough, cough… chocolate milk) mug!  This pot has found its forever home.

Tall Mugs with Leaf Handles

For these two mugs, during the leather hard stage, I added rough textures to the outside and smooth leaf shapes for handles.  My goal was for the outside have a darker bark like surface and have it contrast with a bright glossy smooth surface on the inside and handles. To start learning about my new glazes, I used Amaco Textured Amber for the mug on the left and Amaco Salt Buff for the mug on the right.  On both mugs, I applied Coyote Crazed Copper on the insides and handles.  I wanted a stark contrast between the glossy and the matte surfaces.  My plan was for the glazes to soften the bark textures but not to completely cover them.

The Crazed Copper came out how I expected.  It is a fluid glaze, doesn’t show drips and brush marks, slightly transparent, glossy, and darkens where it pools into lines and textures. This glaze has a lot of promise and I’m looking forward to doing more experiments to learn how this glaze responds over various slips and mason stains.

For the outside of the mugs, the Textured Amber ended up much darker and glossier than I expected and there is almost no color variation. Interestingly, the Salt Buff did the exact opposite.  It has a very dry surface and the yellowish brown color darkens into a murky green when it pools into the crevices. When I glazed these mugs, I was hoping for a surface that was somewhere between the glossy Textured Amber and the dry matte Salt Buff.

On the Textured Amber mug, just below the rim, I found a gem.  The Crazed Copper flowed over the Textured Amber and surprisingly the Copper color remained.  Due to the fluidity of both glazes, the overlap flowed into the texture (Figure 3).  Used on the right shape and texture this could be a very interesting effect.  It will take some more testing to really understand what it will do but for now it is worthy of a note.

Along with the glazes, I also like to analyze the shapes, the feet, and how well the handles function.  For me, the handles are larger than I prefer.  The leaf shapes are a bit thick to use as a handle.  When I was adding the handles, they did seem too wide to be functional but visually I liked how they imitated a leaf shape (Figure 4).  Oh, the balance of beauty and function.

I also noticed that both mugs lost their “fullness” when I added the outside textures. What I mean is that while looking at them, I don’t sense their energy or their inside volumes.  A professor of mine, John Gill, once told me to make certain my pots have a full breath of air.  I wasn’t successful in that aspect with these pieces.  To me, they look to be exhaling.  This gives me an idea for future work.  I want to experiment with putting the pieces back on the wheel after I add the texture to give one more push outwards from the inside.  I’m pretty certain this will restore the inside volume and give the inside a full breath to hold. This final outward push will also stretch the textures and give more variations and more interesting surface.

Large Textured Bowl

On this 12” high bowl, I had used a trimming tool to create a sort of chattering texture on the outside.  My goal in glazing was to emphasize this texture and to then try another glaze on the inside as a liner glaze.  For the outside I applied Coyote Crazed Copper, hoping it would be darker in the crevices and more transparent on the peaks of the texture.  On the inside I applied a thick coating of Amaco Frosted Melon, hoping it would be satin to glossy and a nice surface to use as a serving dish. 

I am pleased with the surface of the Crazed Copper but it didn’t emphasize the texture as I had hoped.  In the future I will either use a more satin glaze that moves with the texture, or use an oxide under this glaze to help highlight the texture. 

The glaze I applied to the inside, I expected to result in a satin surface with an off white color.  Since I used a red clay for this bowl, I knew there would be some interaction between the glaze and the iron in the clay.  Sure enough, the iron seeped into the glaze and created a yellow tint.  In the future, I need to be aware of this color change when I pair it with other glazes.  The surface of this glaze also turned out dryer than I prefer for a liner glaze. It’s not a texture I would enjoy serving food from so instead of a serving dish I would use it as a planter or display piece.

Frosted Melon didn’t turn out how I hoped but it has caught my interest as a glaze worth more testing.  I like how it responded to the iron in the clay though I think the iron may have caused the drier surface.  The next test is to use this glaze on a clay with less iron (stoneware). I’m also curious how this glaze will respond when applied either over or under other glazes.  There is still a lot to learn.

Small Textured Bowl

For this smaller bowl, my goal was to see how to overlap two glazes to add further texture to a piece. I applied Amaco Frosted Melon to the entire piece, inside and outside.  Once that coat was dry, on the outside I lightly rubbed a sponge over the middle textured section to remove the Frosted Melon glaze from the texture peaks and left it remaining in the crevices.  I then overlapped a layer of Crazed Coper over the middle and lower sections.  After that layer dried I used a trimming tool to scrape a texture through the two glazes on the bottom section to create a texture in the glaze itself.

Again, I was expecting Frosted Melon to be a satin surface with an off-white color but this piece was also made with a red clay.  It is satin but to my surprise it not only has a yellow tinge but the yellow is not consistent.  There is a flash of yellow that is more prominent on the rim of the bowl and darker on one side.  I didn’t expect to see flashing from an electric kiln so this is a really nice surprise.  On the inside this glaze has a green tinge that echoes the glossy green on the outside and this similarity of color helps to visually pull the piece together.

The outside of the bowl has two nice textures.  The trick of rubbing the Frosted Melon off of the texture peaks and then overlaying Crazed Copper, created a nice fluid texture that has a lot of movement (Figure 5).  The bottom of the bowl, where I scratched lines through the glazes, has a nice grass like texture with a variety of colors created due to the different thicknesses of the two glazes (Figure 6).

I’m definitely excited about re-creating these textures on future pieces. The bottom texture would not be nice on the inside of a bowl but I do like it on the outside.  It is a nice texture to hold.  These two glazes work well together.  They overlap nicely creating a new texture and they provide a nice contrast of glossy and satin surfaces. I will definitely use this combination again.

Small Textured Bowl

With this bowl I continued to experiment with Coyote Crazed Copper over textures.  This time, before I applied the glaze, I first applied some magnesium oxide to the outside surface.  As I did with the previous small bowl, after the oxide dried, I rubbed it off the peaks and let it remain in the crevices.  I then applied Crazed Copper to the entire bowl, inside and outside.  That was it, a pretty straight forward experiment to see if the magnesium would help to accentuate the texture.

This test was a success!  The Crazed Copper became very fluid, mixed with the magnesium, and created brown rivers flowing around the texture (Figure 7).  The shape also came out nicely.  The shape of the lip and foot echo each other giving a start and end to the piece.  The body is full of volume and has a full breath of air.

This is a combination I will continue using.  Future experiments will be to determine how it works when paired with other glazes.



Small Bowl with Flower Motif

As much as I was enjoying being back in the studio, my daughter was not as fond of my new activity.  She was not accustomed to Mommy leaving and she did not approve.  To help her understand where I was going she first got an “only in Daddy’s arms” visit to the studio (Carey is a very kind soul).  This helped her to understand where I was going and the best part was she loved it there and wanted to join in! 

To help her feel included I talked to her about what I was making and let her hold the pieces ready to be glazed.  After she helped me glaze (see above) I then talked to her about what I could make for her.  Since one of her favorite activities is helping me in the kitchen, we decided she needed her own utensil holder for her spoons, spatula, and whisk.  I don’t remember if she or I suggested butterflies but either way, butterflies it was. 

Since she’s four and rather concrete I knew it would need to be a somewhat realistic butterfly.  I also knew she liked Monarch butterflies the best.  Other butterflies have been dismissed by her in the past as not good enough. This is why this bowl exists. 

I needed to experiment with the new bright color glazes to see if I could pull off Monarch-like colors. I needed to know how they would work over textures and how they would blend with each other.   At the time this bowl was in the leather hard stage and my goal was to add a simple texture like the bowls above. Instead I decided to dedicate this bowl to collecting as much information as possible.  It was going to become a rather busy piece.

I used three different tools, created three different patterns, and left the inside and lip smooth.  For the glazing, I went over the top and used six glazes.  Several of the glazes use the same base but different colorants so I was pretty confident they would work well together.  What I didn’t know, and wanted to find out, was would they blend together when overlapped or would the top glaze be so opaque it would hide the bottom glaze.

On the inside and lip I first brushed on Baby Blue Satin and let it dry.  I then used Buttercup to paint a design over the Baby Blue, let it dry, and then scratched another design through both glazes to create a texture.   On the outside there where three textures.  The flower motifs, the background, and the bottom section.  For the flowers, I used overlapping brushstrokes with Really Red, Coral Satin, and Buttercup.  I wanted to see if these colors would blend together, if the bottom glazes would show through, and if the brush marks would remain.  I knew these glazes would have a glossy finish so I picked a satin glaze (Cerulean Satin) to apply to the background.  I wanted to find a glaze that would soften the background texture, allowing the glossy flowers to be more prominent.  Lastly, I used the Crazed Copper on the bottom panel.  I viewed this panel as the grass or flower stems and wanted a greenish color so Crazed Copper it was.

The end results are the Baby Blue is still rather dry, I doubt I'll use this glaze for functional ware, and the Buttercup over the Baby Blue was opaque with very little movement. The scratch through design didn’t create any variation in the glaze surfaces or colors.  It did allow the clay to show through since these glazes didn’t move over the scratches (Figure 8).  The Cerulean Satin wasn’t satin.  Instead it is quite glossy.  The texture on the background area is quite small and caused some pin holing with this glaze.  This glaze will work better either on a smooth surface or a larger texture.  The Crazed Copper on the bottom panel definitely enhanced the texture, flowed enough to hide all brush marks, and darkened in the crevices.  The glazes used over the flower textures did not move much and ended up hiding the texture (Figure 9).  They do work well together and they did blend some.  For the most part, the color on the top hid the color beneath.  Due to the opacity and lack of movement with these glazes, it is unlikely I’ll use them over textures any more.  These two qualities prevent them from blending well with textures

What Next?

I chalk that up as a very successful first experiment.  I gathered a ton of information about mid-fire glazes and have plenty of ideas to move forward.  To keep the Hardie household happy, the main topic is the butterfly vessel for Laney.  I’m going to play around with some butterfly designs, textures, and shapes.  For the glazes, the flower bowl gave me enough information to know I want to move forward with the bright colors but I need different glazes that are more fluid and transparent.  

So, I have to go now.  I need to go shopping :-).

Detail Images

Figure 1

Overlapping a thick coat of Coyote Buttercup over Coyote Baby Blue Satin

Figure 2

Overlapping of a thin coat of Coyote Buttercup over Coyote Baby Blue Satin

Figure 3

Coyote Crazed Copper over Amaco Textured Amber

Figure 4

Coyote Leaf handle

Figure 5

Coyote Crazed Copper over Amaco Frosted Melon

Figure 6

Coyote Crazed Copper over Amaco Frosted Melon

Figure 7

Coyote Crazed Copper over Magnesium oxide

Figure 8

Coyote Buttercup over Coyote Baby Blue Satin

Figure 9

Coyote Really Red, Coral Satin, and Buttercup.  Background is Coyote Cerulean Satin