Building a Weathered Surface Angelo di Petta

Appears in the Jul/Aug 2022 issue of Pottery Making Illustrated.

Like a lot of potters and ceramic artists, I pretty much stumbled into working with clay. I didn’t know much about it when I entered art school. My interest in architecture motivated me to pursue studies in interior design.

One of the required courses in my first year was an introduction to the craft studios. This involved five-week sessions in ceramics, metal, wood, and fiber. I enjoyed this introduction to materials and processes so much that it became clear to me that working with my hands as well as my head gave me great satisfaction. So, I abandoned my desire to study interior design. In my second year of studies, metal was my favorite medium, but by the end of my fourth year, I was fully immersed in the ceramics studio and graduated with a major in ceramics.

A turning point for me was a third-year class visit to a sewer-pipe factory. Enormous lengths and diameters of clay pipe were being extruded. Seeing this changed my ideas about how clay should be formed and what clay objects should look like. My fourth year was spent making dies and extruding stoneware and porcelain forms. 

In the mid 1970s, I spent a year in Faenza, Italy—a center of pottery production and majolica since the 13th century—studying ceramic design and production processes. Earthenware was the dominant clay used for functional and decorative objects, tiles, and architectural elements. Imagery plays a very important part in all these applications. So it was there that my journey with low-fire clays and the use of molds began.

Inspiration

The natural and built environment are a major inspiration and influence on the work that I make. I see ceramic forms and surfaces in everything around me; abandoned buildings, layers of paint peeling off concrete walls, insect-eaten bark on trees, polished beach stones, etc. This is all visual information that eventually finds its way into my work. Each piece I make is an exploration of the natural process of weathering and the gentle wearing away of surfaces by water and sand. This process reveals layers of colors. The patterns suggest some other mysterious activity. My etching process mimics natural phenomena.

Casting Slips

I use several types of casting-slip in my studio, including a red and a white earthenware, mid-range porcelain, and black stoneware. Red and white earthenwares are my preferred clays. I have used them since the 1970s for small functional and sculptural objects as well as large architectural installations. 

In the early 1970s, reduction-fired stoneware ruled. Earthenware was considered hobby clay. But I liked the fact that it could be fired at lower temperatures. And since it had no otherwise outstanding visual qualities, it could be considered a blank canvas for an infinite variety of surface treatment and imagery. 

I use Red Earthenware Casting Slip 805 made by Pottery Supply House in Oakville, Ontario. It has very good casting qualities, is smooth, and has a warm terra-cotta color when fired to cone 04. It casts a bit slower than white earthenware and porcelain.

Slip Casting the Forms

Since I discovered slip casting, using molds has been my preferred method of making forms. I enjoy the process of thinking through how I will make the model and the mold of the imagined form. Forms can be made this way that would normally be more difficult to create using other methods. Once the mold is made, I can make as many copies of the form and embellish them in a variety of ways to create one-of-a-kind pieces. Molds can be used for slip casing, press molding, and combinations of both.

To make a small vessel from a two-piece mold, pour red-earthenware casting-slip into a plaster mold and leave it for about 20 minutes (1). The plaster absorbs water from the slip. This process results in the build-up of a clay wall against the inside of the mold. Drain the mold of the remaining, non-absorbed slip when the desired thickness is achieved (2), then flip the mold upside down for a few minutes so that the slip fully flows out. After 15 minutes, turn the mold back over, trim the top (3), and allow it to sit until the cast releases from the mold and can be removed (4). Once the cast form is dry, clean it with a damp sponge to remove any sharp edges or unwanted marks.

Designing the Surface

I have used the etching process for many years, but what inspired this particular series was the plastic netting that I found on cartons of clementines. It seemed like the perfect material—simple cut-out pattern, thin, flexible, reusable, and free. It worked very well with the layering of colors and patterns. My goal was to create as much visual activity as possible on a limited surface.

Etching the Surface

The first step to creating the surface is to layer many colors of underglazes on to the greenware piece. I start with a black layer to coat the entire exterior of the form (5). Then, I use blue, turquoise, red, yellow, and orange layers in random patterns. I use masking tape and stencils to create these shapes (6). The lighter colors are used last (7). I apply one coat of each color of underglaze. I prefer the consistency of the underglaze to be thicker rather than flowing and use a soft ¾- or 1-inch brush to apply it. This gives me a smooth surface. I allow the layers to dry between coats. 

The next step is to create the relief patterns. This is done by etching, essentially wiping away to reveal the layers of colors. I use a masking material, in this case the plastic netting that comes with boxes of clementines. The netting is stretched over the form (see 8), taking care not apply too much pressure that could break the greenware. I then use a damp sponge to gently wipe away the underglaze layers until the black layer or the base clay is revealed (8). The neat part of this process is the control one has as to how much to etch, or how little.

Finishing the Surface

When I feel the etching is complete, I apply 3 or 4 coats of red terra sigillata to seal the bottom. The piece is then ready to be bisque fired to cone 04 (9).

After the bisque firing, I apply a commercial liner glaze to the interior (10) and a clear glaze over the etched exterior (11). The glaze firing is taken up to cone 06. 

Angelo di Petta’s home and studio are located in the rolling countryside near Millbrook, Ontario, Canada. He graduated from the Ontario College of Art (now OCAD University), and for 46 years has shared his knowledge of ceramics, model and mold making, and design through teaching, lectures, mentorships, and workshops. To see more of Angelo’s work, visit dipetta.com and @angelodipettaceramics on Instagram.