I’ve been drawn to simple forms that showcase the beauty and richness of surface and texture of clay and raw earth materials since participating in my first wood firing over 20 years ago. The works that were buried deep in the ashes of the firebox were crusty and textured, looking as if they were excavated from the depths of an ancient ocean. I’ve been searching for that same feeling in my work, a connection to the sense of beauty and deep time, ever since.
This bowl, in my Caldera Series, is one of my favorite forms. When I get the curve of the walls and the edge cut and textured just right, paired with the curved bottom, it strikes a beautiful tone. It balances the raw with the refined, a grounded weight and strength with lift and delicacy, both masculine and feminine.
Form a Hump Mold
Let’s start by planning the shape and approximate size of the bowl, and then making a bisque slump form a bit wider than the final bowl form will be, and with the curve you desire for the bottom of the form. First, build a hump shape out of scrap clay on a board with the curve that you want, but slightly wider. Let it dry mostly, then lightly compress a slab over it. After it dries enough to hold its shape but not crack from shrinkage, pop it off, let it dry, and bisque fire it. I keep many sizes and shapes of these in the studio (1, see 14).
Build a Caldera Bowl
Use a sturdy, groggy stoneware clay (I like a dark body for glaze depth) and roll out a slab that is approximately ½ inch (1.3 cm) wider than you want for your base. Make the form thick to allow you to scrape it down to size later in the process, thus giving you flexibility to adjust the shape and scrape in lots of texture as you go. Compress the slab with a metal rib in multiple directions, add grog (I use 10-mesh grog or a 10–20-mesh mix) to only the top side of your slab, and compress it into the slab (2). Add a sprinkle of grog to your slump mold before carefully flipping and laying your slab into the mold (3). Compress the slab and then cut it to size (image shows a 15-inch (38.1-cm)-wide base) (4).
Next, roll out ½-inch (1.3-cm)-thick (or a bit less) slabs for your walls. Making them approximately 6 inches (15.2 cm) wide by 15 inches (38.1 cm) long, cut them in half length-wise to make two walls (5). You may need three slabs to go around, depending on the size.
Score and slip the edges, then attach them by using the extra thickness of the slabs to push the wall strongly into the base, getting a good connection (6). Attach the slabs to one another as you add a new wall. Building the bowl in one session makes it easier to attach while the clay is soft, giving the flexibility to just overlap the seams a bit—press them strongly together, and scrape to compress—no beveling or too much fussing (7).
After you have attached all of the walls, compress a coil into the inner seam to create a nice, continuous curve between the wall and the base, and to make the connection stronger (8). At this point, you can start making little adjustments to your form as you go, curving the wall slightly inward and working the bottom outer edge into the wall curve (9).
Cut the lip of your bowl to shape (10). Try a simple double-dip as shown here, or a triple, or cut a more symmetrical and sculptural lip.
Adding Texture and Shaping
Now comes the messy part! Wearing a respirator, add grog to the exterior of the form, then use your rib to scrape it into the surface. Scrape and lift up the wall, always supporting the opposite side of your wall with your other hand as you go. Use your rib to pick up grog and apply to the exterior (11). This action embeds the grog, ripping at the surface to create texture and tapering the wall thickness as you go round and round the piece (12). Note: I recommend keeping a strong curve/bend and about a 45° angle of the rib while scraping.
Add grog to the interior and repeat the adding and scraping of grog action while you support the form with your other hand on the exterior (13).
Now is a great time to take a break! That was a lot of scraping. It’s best to build the form all in one day and get the grog into the soft surface. Then, cover it with plastic overnight and come back to a slightly stiffer piece the next day.
Alright, back to more scraping. Now you are going to get a bit more aggressive, removing more clay as you scrape, tapering the wall thickness, adjusting the profile curve, and creating a nice rough texture on the surface. Keeping your clay fairly soft is helpful to getting a heavier texture with your grog. Add grog liberally as you keep scraping round and round, when spots start to smooth out.
To create a textured lip, support the opposite edge of the lip with your other hand, scrape upward at around a 45° diagonal, adding more grog to the edge if you want an extra textured edge. Do this to both the inside and outside, slowing your speed down as you do another round and being more attentive as you keep working the now delicate edge. You will be ripping it a bit and removing clay from the top inch (2.5 cm), re-cutting the edge from time to time as the thinning alters the shape (14).
Step back often to look and adjust, re-cut, reshape the profile, add grog and rip in more texture, thin the walls down more, etc.
Drying and Finishing
Once it feels finished, dry it slowly with fabric and plastic while leaving it in its slump mold. Once it is beyond leather hard (no flex in the form when you lift) but not bone dry, lift it carefully, taking care of the top edge, and rest it on its side on top of a nice bed of foam. Keep it at a slight angle so the pressure is toward the bottom of the piece, not on the lip. Using a metal rib, scrape a slightly concave, minimal foot on the bottom. Use a kiln shelf, or a piece of one, to level the foot. Place the bowl on the shelf and move it around as if you are sanding a flat spot on the bottom. Find where the scratched marks are and, using your rib, scrape the clay away in these spots. Do this multiple times until your bowl sits level (15).
This type of bowl tends to slump slightly during firing, so create some coil props to help support the outer weight (16). Make sure your coils sit about ¼–½ inch (0.6–1.3 cm) back from the edge of your bowl so it won’t come in contact with the exterior glaze—the underside will only have a slip applied. Press the coils under the bowl to get the right shape, poke some holes in them to dry quickly, and pull them away from the bowl to dry so the moisture doesn’t transfer to your piece.
Firing and Glazing
When all is dry, load your bowl into the kiln first, then slide props in on each side, pushing them under the piece to lift it just the slightest bit. Check for wobble and adjust. This ensures the piece is supported through most of the firing, even with shrinkage.
After the bisque firing, using a damp sponge, lightly wipe the surface to get off excess grog and dust. For glazing, brush on two coats of black slip on the entire underside, then brush 2–3 coats of glaze on the exterior and interior (thin the glaze with water for the first coat to get it into the texture). I use Spectrum 1412 Charcoal Shino for a food-safe black. Thicker application results in more black and the slow cooling of the kiln creates a more matte surface (see firing schedule above).
Again, place your bowl in the kiln, slide in the clay props, and double check that the props are around ½ inch (1.3 cm) away from the glazed edge.
I use this same building/texturizing technique in many different forms, from long rectangular trays, oval-shaped bowls, and taller forms using tall slab walls or building up by coiling. You can also try a variety of grogs, such as Gran-i-Grit (a low-iron chicken grit!) or make your own by crushing up dry clay and bisque firing it.
Erica Iman is a full-time ceramic artist and painter in Lawrence, Kansas. Between earning her BFA and MFA, she served two years in the US Peace Corps on the Eastern Steppe of Mongolia and was a selected participant in the International Workshop for Ceramic Arts in Tokoname (IWCAT) Japan program. To learn more, visit www.ericaiman.com.
We understand your email address is private. You will receive emails and newsletters from Ceramic Arts Network. We will never share your information except as outlined in our privacy policy. You can unsubscribe at any time.
You have read of of your complimentary articles for the month.
For unlimited access to Pottery Making Illustrated premium content, please subscribe.
We understand your email address is private. You will receive emails and newsletters from Ceramic Arts Network. We will never share your information except as outlined in our privacy policy. You can unsubscribe at any time.
Subscribe to Pottery Making Illustrated
I’ve been drawn to simple forms that showcase the beauty and richness of surface and texture of clay and raw earth materials since participating in my first wood firing over 20 years ago. The works that were buried deep in the ashes of the firebox were crusty and textured, looking as if they were excavated from the depths of an ancient ocean. I’ve been searching for that same feeling in my work, a connection to the sense of beauty and deep time, ever since.
This bowl, in my Caldera Series, is one of my favorite forms. When I get the curve of the walls and the edge cut and textured just right, paired with the curved bottom, it strikes a beautiful tone. It balances the raw with the refined, a grounded weight and strength with lift and delicacy, both masculine and feminine.
Form a Hump Mold
Let’s start by planning the shape and approximate size of the bowl, and then making a bisque slump form a bit wider than the final bowl form will be, and with the curve you desire for the bottom of the form. First, build a hump shape out of scrap clay on a board with the curve that you want, but slightly wider. Let it dry mostly, then lightly compress a slab over it. After it dries enough to hold its shape but not crack from shrinkage, pop it off, let it dry, and bisque fire it. I keep many sizes and shapes of these in the studio (1, see 14).
Build a Caldera Bowl
Use a sturdy, groggy stoneware clay (I like a dark body for glaze depth) and roll out a slab that is approximately ½ inch (1.3 cm) wider than you want for your base. Make the form thick to allow you to scrape it down to size later in the process, thus giving you flexibility to adjust the shape and scrape in lots of texture as you go. Compress the slab with a metal rib in multiple directions, add grog (I use 10-mesh grog or a 10–20-mesh mix) to only the top side of your slab, and compress it into the slab (2). Add a sprinkle of grog to your slump mold before carefully flipping and laying your slab into the mold (3). Compress the slab and then cut it to size (image shows a 15-inch (38.1-cm)-wide base) (4).
Next, roll out ½-inch (1.3-cm)-thick (or a bit less) slabs for your walls. Making them approximately 6 inches (15.2 cm) wide by 15 inches (38.1 cm) long, cut them in half length-wise to make two walls (5). You may need three slabs to go around, depending on the size.
Score and slip the edges, then attach them by using the extra thickness of the slabs to push the wall strongly into the base, getting a good connection (6). Attach the slabs to one another as you add a new wall. Building the bowl in one session makes it easier to attach while the clay is soft, giving the flexibility to just overlap the seams a bit—press them strongly together, and scrape to compress—no beveling or too much fussing (7).
After you have attached all of the walls, compress a coil into the inner seam to create a nice, continuous curve between the wall and the base, and to make the connection stronger (8). At this point, you can start making little adjustments to your form as you go, curving the wall slightly inward and working the bottom outer edge into the wall curve (9).
Cut the lip of your bowl to shape (10). Try a simple double-dip as shown here, or a triple, or cut a more symmetrical and sculptural lip.
Adding Texture and Shaping
Now comes the messy part! Wearing a respirator, add grog to the exterior of the form, then use your rib to scrape it into the surface. Scrape and lift up the wall, always supporting the opposite side of your wall with your other hand as you go. Use your rib to pick up grog and apply to the exterior (11). This action embeds the grog, ripping at the surface to create texture and tapering the wall thickness as you go round and round the piece (12). Note: I recommend keeping a strong curve/bend and about a 45° angle of the rib while scraping.
Add grog to the interior and repeat the adding and scraping of grog action while you support the form with your other hand on the exterior (13).
Now is a great time to take a break! That was a lot of scraping. It’s best to build the form all in one day and get the grog into the soft surface. Then, cover it with plastic overnight and come back to a slightly stiffer piece the next day.
Alright, back to more scraping. Now you are going to get a bit more aggressive, removing more clay as you scrape, tapering the wall thickness, adjusting the profile curve, and creating a nice rough texture on the surface. Keeping your clay fairly soft is helpful to getting a heavier texture with your grog. Add grog liberally as you keep scraping round and round, when spots start to smooth out.
To create a textured lip, support the opposite edge of the lip with your other hand, scrape upward at around a 45° diagonal, adding more grog to the edge if you want an extra textured edge. Do this to both the inside and outside, slowing your speed down as you do another round and being more attentive as you keep working the now delicate edge. You will be ripping it a bit and removing clay from the top inch (2.5 cm), re-cutting the edge from time to time as the thinning alters the shape (14).
Step back often to look and adjust, re-cut, reshape the profile, add grog and rip in more texture, thin the walls down more, etc.
Drying and Finishing
Once it feels finished, dry it slowly with fabric and plastic while leaving it in its slump mold. Once it is beyond leather hard (no flex in the form when you lift) but not bone dry, lift it carefully, taking care of the top edge, and rest it on its side on top of a nice bed of foam. Keep it at a slight angle so the pressure is toward the bottom of the piece, not on the lip. Using a metal rib, scrape a slightly concave, minimal foot on the bottom. Use a kiln shelf, or a piece of one, to level the foot. Place the bowl on the shelf and move it around as if you are sanding a flat spot on the bottom. Find where the scratched marks are and, using your rib, scrape the clay away in these spots. Do this multiple times until your bowl sits level (15).
This type of bowl tends to slump slightly during firing, so create some coil props to help support the outer weight (16). Make sure your coils sit about ¼–½ inch (0.6–1.3 cm) back from the edge of your bowl so it won’t come in contact with the exterior glaze—the underside will only have a slip applied. Press the coils under the bowl to get the right shape, poke some holes in them to dry quickly, and pull them away from the bowl to dry so the moisture doesn’t transfer to your piece.
Firing and Glazing
When all is dry, load your bowl into the kiln first, then slide props in on each side, pushing them under the piece to lift it just the slightest bit. Check for wobble and adjust. This ensures the piece is supported through most of the firing, even with shrinkage.
After the bisque firing, using a damp sponge, lightly wipe the surface to get off excess grog and dust. For glazing, brush on two coats of black slip on the entire underside, then brush 2–3 coats of glaze on the exterior and interior (thin the glaze with water for the first coat to get it into the texture). I use Spectrum 1412 Charcoal Shino for a food-safe black. Thicker application results in more black and the slow cooling of the kiln creates a more matte surface (see firing schedule above).
Again, place your bowl in the kiln, slide in the clay props, and double check that the props are around ½ inch (1.3 cm) away from the glazed edge.
I use this same building/texturizing technique in many different forms, from long rectangular trays, oval-shaped bowls, and taller forms using tall slab walls or building up by coiling. You can also try a variety of grogs, such as Gran-i-Grit (a low-iron chicken grit!) or make your own by crushing up dry clay and bisque firing it.
Erica Iman is a full-time ceramic artist and painter in Lawrence, Kansas. Between earning her BFA and MFA, she served two years in the US Peace Corps on the Eastern Steppe of Mongolia and was a selected participant in the International Workshop for Ceramic Arts in Tokoname (IWCAT) Japan program. To learn more, visit www.ericaiman.com.
July/August 2025: Table of Contents
Must-Reads from Pottery Making Illustrated
Unfamiliar with any terms in this article? Browse our glossary of pottery terms!
Click the cover image to return to the Table of Contents