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IV 50 plates

Craft, clay and kiln

Digging, throwing, glazing and firing: the steps, the tools and the materials, plus the flaws that teach.

A spade and bucket beside a cut bank of reddish clay. — 001Digging clay Traditionally clay was dug from pits near the pottery. Its make-up varies from place to place, which is why the ware has a regional character. General description; not confirmed to a single source.

Lumps of dry clay dissolving in a large tub of muddy water. — 002Soaking clay to slip Dry clay is soaked until it breaks down into a liquid paste. This lets stones and roots be separated out before it is dried to a workable state. General description; not confirmed to a single source.

Wet clay being pressed through a round mesh sieve over a bucket. — 003Sieving clay slip The slip (liquid clay) passes through a fine sieve that holds back sand, roots and lumps. It is then left to stiffen on plaster or in the sun until it can be kneaded. General description; not confirmed to a single source.

Hands pressing and rolling a block of clay on a wooden bench. — 004Wedging clay Wedging clay by hand evens out the moisture and drives out air. Air bubbles can damage a piece in the kiln, which is why it is a usual step before throwing.

A row of small fired clay test tiles in graded shades. — 005Clay test tiles Small test pieces show how a clay shrinks, what colour it fires to and how it takes glaze. Each records one clay in one firing. General description; not confirmed to a single source.

Rows of round clay balls on a board under a damp cloth edge. — 006Weighed clay balls Before throwing, clay is cut and weighed into balls so that pots of one kind come out at similar size. The balls are kept covered so they do not dry. General description; not confirmed to a single source.

Two wet hands bracing a spinning mound of clay. — 007Centring on the wheel Centring brings the clay to run true on the spinning wheel head. It is the first step of throwing and needs steady pressure from both hands and the body. General description; not confirmed to a single source.

Thumbs pressing into the centre of a spinning clay mound. — 008Opening the clay After centring, the thumbs or fingers press down to open the clay and set the floor of the pot. The wall is then drawn upward from this base. General description; not confirmed to a single source.

One hand inside and one outside a tall clay cylinder on the wheel. — 009Pulling up the wall Pulling raises and thins the wall of a pot in several passes, one hand inside and one outside. Each pass makes the form taller and more even. General description; not confirmed to a single source.

A heavy wooden wheel with a flywheel in a rustic workshop. — 010Treadle potter's wheel Before electric motors, wheels were turned by hand or by foot. In Malhada Sorda, for instance, the low wheel turns slowly with the foot on a wooden crosspiece. General description; not confirmed to a single source.

A tall jar made of stacked thrown sections with visible joins. — 011Throwing a large jar Very large jars are often thrown or built in stages, with each section left to stiffen before the next is added. This keeps tall walls from slumping. General description; not confirmed to a single source.

A twisted wire drawn beneath a small bowl on the wheel. — 012Cutting off with a wire A thin wire drawn under the base frees a finished pot from the wheel head. Cutting also shows the thickness of the floor, which should be even. General description; not confirmed to a single source.

A steel loop tool shaving curls of clay from an upturned pot. — 013Turning leather-hard pots Trimming a leather-hard piece refines its shape and lightens the foot. The clay is firm enough to hold its form yet still soft enough to cut. General description; not confirmed to a single source.

The underside of a plate showing a freshly trimmed foot ring. — 014Trimming a foot ring A foot ring is a low ridge cut on the base that lifts a pot off the table and gives the glaze a clean edge to stop at. Its shape varies with the tradition. General description; not confirmed to a single source.

A wet hand stroking a tapering strip of clay downward from a lump. — 015Pulling a handle A strip of clay is pulled between wet fingers into a tapering handle and left to stiffen slightly. It is then curved to suit the pot it will join. General description; not confirmed to a single source.

A hand pressing a handle onto a jug with a scored joint. — 016Attaching a handle Handle and body are scored and painted with slip so they bond. The joint is then smoothed. If it is badly made, it can crack as the pot dries or fires. General description; not confirmed to a single source.

A clay pot with a lid lifted to show the inner ledge. — 017Fitting a lid Lids are made to sit on a gallery, a small inner ledge on the pot. The lid and pot are best fitted while both are still clay and kept together for firing. General description; not confirmed to a single source.

A hand dipping a jug into a bucket of white slip. — 018Dipping in slip Engobe (slip) is a clay-based coating applied to a piece by dipping, pouring or brush. It changes the surface colour and gives a base for decoration.

A metal point scratching a line through white slip on a dark bowl. — 019Sgraffito In sgraffito, the design is scratched with a point through a layer of slip to show the clay beneath. The piece is then glazed. General description; not confirmed to a single source.

A brush painting a stroke of blue on a white plate. — 020Brush decoration Painting with slip or oxide pigments is done in a few confident strokes with a soft brush. A skilled hand repeats the same stroke across many pieces. General description; not confirmed to a single source.

A cut paper stencil lying on a plate being daubed with colour. — 021Stencil decoration A stencil is a plate cut out with the motif, which in tile work may be metal. Colour brushed over it passes only through the openings, so patterns repeat quickly.

A pricked paper pattern and a dusty pounce bag over a tile. — 022Pounce transfer A drawing on paper is pricked along its lines and a charcoal-powder pad is passed over it, leaving dotted outlines on the tile. The painter then follows those marks. General description; not confirmed to a single source.

A smooth pebble rubbing the shoulder of a red clay pot. — 023Burnishing with a stone Burnishing is polishing leather-hard clay with a smooth object, such as a stone, until it gains a sheen. There is no glaze; the shine comes from polishing alone. General description; not confirmed to a single source.

Black pots in a smoky earth-covered kiln at dusk. — 024Black firing in smoke For black ware, the kiln is smothered with earth and the atmosphere is reducing, which turns the pieces black. In Bisalhães the fuel is broom, pine needles and heather.

A group of matt-and-gloss black jugs and bowls on a board. — 025Black pots Black ware ranges from metallic grey to black, the result of reduction firing. It is associated with Bisalhães (Vila Real), inscribed by UNESCO in 2016, and with Molelos (Tondela).

Hands placing dry pots in a stack inside an open kiln. — 026Loading the bisque kiln Dry pieces are loaded for the first firing, which produces the chacota (bisque). At this stage they can touch, because there is no glaze yet to stick them together.

Pale bisque bowls and jars arranged on a plain table. — 027Bisque ware Chacota is the first firing of ceramics that will be glazed. The piece comes out hard but still porous, ready to take glaze.

A hand stirring a bucket of thick white glaze with a ladle. — 028Mixing glaze Glaze is a mixture of powdered minerals and water, stirred and sieved until creamy. It needs frequent stirring, because the solids settle. General description; not confirmed to a single source.

A bowl held with tongs being dipped into white tin glaze. — 029Dipping in tin glaze Tin glaze is white, glossy and opaque, thanks to tin oxide. It is usually applied to earthenware by dipping the bisque-fired piece briefly.

A sponge wiping the base of a glazed plate. — 030Wiping the foot Before firing, glaze is sponged off the foot. Otherwise it melts and glues the piece to the kiln shelf. General description; not confirmed to a single source.

Rows of glazed test tiles in varied colours on a tray. — 031Lead-free glaze tests Today's workshops often use lead-free glazes, tested first on small pieces for colour, gloss and fit. Lead is a health risk and its release from food ware is regulated. General description; not confirmed to a single source.

Flames glowing in the firebox of a brick kiln beside stacked wood. — 032Wood-fired kiln A wood kiln burns wood in a firebox, and flame and hot gases pass through the chamber. The temperature rises slowly over many hours. General description; not confirmed to a single source.

An octagonal front-loading kiln with a closed lid and a controller. — 033Electric kiln An electric kiln heats with elements in its walls. Firing is clean and easy to control and repeat, which is why many modern studios use one. General description; not confirmed to a single source.

A tall brick bottle kiln beside a small factory yard. — 034Bottle kiln A brick kiln named for its shape, a type common in England until the 1960s. The one at the Museu de Cerâmica de Sacavém, in Loures, is about 12 m tall and can be visited. General description; not confirmed to a single source.

Three pyrometric cones, one melted and bowed, on a pad. — 035Pyrometric cones Small ceramic cones soften and bend at a set temperature and serve as a gauge. Seen through a spy hole, they show how far the heat has gone. General description; not confirmed to a single source.

A kiln door open on shelves of glazed bowls and jugs. — 036Unloading the kiln Unloading means taking the pieces out of the kiln once it has cooled. They are checked one by one for defects and glaze problems.

Rows of unfired jugs and bowls drying on wooden planks. — 037Drying shelves Thrown and trimmed pots are dried slowly on shelves, often turned and covered at first, so they do not warp or crack. Fast drying is a leading cause of loss. General description; not confirmed to a single source.

A press forming a square tile blank from a lump of clay. — 038Pressing tiles In factories, clay or powder is pressed in a mould, dried and fired. A tile fired once is called a biscuit, or chacota. General description; not confirmed to a single source.

Neat stacks of unglazed square tile blanks. — 039Tile biscuits (chacota) A tile fired once, before glazing, is called a biscuit, or chacota. Only one face is glazed afterwards.

A brush painting blue petals on a powdery white tile. — 040Painting a tile In tin-glaze tile painting, colours are brushed onto a raw white glaze surface that cannot be corrected. Pigment sinks in as the glaze fuses, so each stroke must be sure.

Small pots of blue and brown pigment with brushes lying beside. — 041Painter's palette Tile painters keep pigments mixed with water in small pots, and use brushes of different sizes for outline and fill. General description; not confirmed to a single source.

A fan of wooden and metal ribs arranged on a bench. — 042Ribs and scrapers Ribs are flat tools, of wood, metal, rubber or plastic, for shaping, smoothing and scraping clay. Each curve suits a form, and many potters make their own. General description; not confirmed to a single source.

A small group of well-worn pottery hand tools beside a sponge. — 043Wire, needle and sponge A potter's basic kit includes a cutting wire, needle, sponge and other modelling tools. Most are cheap and last for years, polished by use. General description; not confirmed to a single source.

A bundle of brushes of different sizes standing in a jar. — 044Potter's brushes Ceramic brushes hold a lot of liquid so a line can be drawn in one stroke. Hair and bamboo or wooden handles vary by task, from fine liners to wide glaze brushes. General description; not confirmed to a single source.

Four small heaps of coloured powders on a plate. — 045Oxide pigments Ceramic colours come largely from metal oxides: cobalt gives blue, copper green, manganese purplish brown and iron brown. Results shift with the glaze and the firing.

Three bowls of white powders next to lumps of raw mineral. — 046Kaolin, quartz and feldspar Kaolin is the white clay of white bodies, quartz supplies silica and feldspar acts as a flux. Many glazes and bodies combine these materials, depending on the recipe.

A shelf of buckets and tubs filled with differently coloured glazes. — 047Glaze buckets Each glaze is kept in its own bucket, tightly lidded and kept stirred. The colour of the wet glaze rarely resembles the colour it will fire to. General description; not confirmed to a single source.

A glazed bowl with glaze beaded away from bare clay patches. — 048Glaze crawling When glaze pulls back and beads up, it leaves parts of the piece bare (crawling). It is a flaw, shown here for study.

A glossy glaze surface dotted with tiny pits. — 049Glaze pinholes Tiny holes in the glaze surface, like pin pricks (pinholes). They are often blamed on gas escaping from the clay or glaze during firing. General description; not confirmed to a single source.

A white glazed plate crossed by a network of fine cracks. — 050Glaze crazing Crazing, or craquelê, is a network of fine cracks in the glaze, which appears when the glaze contracts more than the clay on cooling. It can be a sought-after effect, but otherwise it is a flaw.

All images are AI-generated illustrations in the manner of the tradition, not photographs of specific objects.