How to care for handmade ceramics: dishwasher, microwave, oven and crazing

A handmade mug or plate is usually tougher than it looks. Most damage comes from three things: sudden changes of temperature, the microwave meeting something it should not, and knocks against other dishes. All three are easy to avoid once you know what your piece is made of.

That is the catch. "Handmade ceramics" covers low-fired earthenware, high-fired stoneware and porcelain, bone china and pieces with real gold on them. A maker who fires stoneware hard may happily say "dishwasher and microwave safe". A maker of soft earthenware or gold-rimmed china will say something different.

So start with the maker's care card or product page. Those instructions override this guide. What follows is drawn from potters' and manufacturers' published care pages and from ceramic science sources, for when you want to understand the reasons.

Key takeaways

• The maker's instructions come first, because clay body, glaze and firing decide what a piece can take.
• Thermal shock is the most common avoidable cause of cracks: do not move ceramics straight from freezer to hot oven, or from oven to a cold surface, and never put them on a hob or open flame.
• Gold, platinum and other metallic decoration should stay out of the microwave, and makers such as Feldspar ask for hand washing.
• A mug that gets hotter than its contents in the microwave is absorbing water, often through an unglazed foot or crazed glaze. Stop microwaving it.
• Crazing (fine cracks in the glaze) is a defect on functional ware. Retire cracked, crazed or deeply chipped pieces from food use and ask the maker.
• Stack with felt or cloth between pieces, because an unglazed foot can scratch the glaze below it.

Know what you have

Ceramic tableware falls into a few broad families, and they behave differently.

Type	How it is made	What it means for care
Earthenware	Fired at lower temperatures and stays porous	Relies on the glaze to hold liquid; more prone to water uptake through bare clay
Stoneware	Fired hotter until dense	Strong and durable, but Digitalfire notes it is more brittle and susceptible to thermal shock than earthenware
Porcelain	Dense, vitrified, often translucent	Low porosity; very vitreous bodies can be the least forgiving of sudden heat
Bone china	Varies by maker	Wedgwood treats it separately from stoneware and porcelain; gold-decorated pieces are often hand wash only

Digitalfire describes earthenware as porous because it does not develop enough glass to fill its voids, and stoneware as semi-vitreous: dense, but not zero porosity. In its informal flame tests, terracotta survived longer than typical stoneware or porcelain before cracking. Porous bodies resist thermal shock better, but they take up water more easily.

Official definitions draw the lines by water absorption. The US Census Bureau's export schedule for ceramics, measured with the ASTM C373 test, defines porcelain and china as absorbing no more than 0.5% of their weight in water, stoneware no more than 3%, and earthenware more than 3%. These are trade classification lines, not care rules, but they show why an earthenware mug needs a sound glaze.

If you do not know the body, ask the maker. The Leach Pottery in St Ives, for example, says its Standard Ware is a stoneware with a small amount of iron.

Dishwasher

Many makers allow the dishwasher, with conditions:

• Mud Australia says its porcelain dinnerware is dishwasher safe and asks you to place each piece so it does not touch others, to avoid chips.
• Wedgwood allows stoneware and porcelain on a gentle cycle, and bone china only if it is marked as dishwasher safe.
• Feldspar says its fine bone china colour collection is dishwasher safe up to 60 °C, recommends liquid or gel detergent because tablets and powder can be abrasive, and says anything with gold is hand wash only.

If a piece has no instructions, hand washing in warm water with washing-up liquid is the cautious default. Mud Australia suggests drying on a rack with space between pieces.

Microwave

Two things go wrong in a microwave: water in the clay and metal on the surface.

Water in the clay. Digitalfire explains that a porous body can soak up water through an unglazed foot or through crazed glaze. In the microwave that water heats, and the piece can get hotter than its contents or even crack. Industrially, 1% porosity is treated as the margin for microwave safety, and Digitalfire notes that a lot of studio ware sits around 2 to 3% and usually copes because the glaze limits water entry. Its quick test: put a little water in the piece and heat it for 30 seconds. If the piece is clearly hotter than the water, there is a problem.

Metal on the surface. Digitalfire notes that gold on bone china conducts electricity and can arc. Wedgwood says items with metallic decoration are not microwave safe. Feldspar says gold-decorated pieces cannot go in microwaves or dishwashers, and notes that its hand-painted gold is real gold. Mayco, a glaze supplier whose overglazes potters use, says ware decorated with its gold overglazes should not be used in a microwave. Digitalfire also lists glazes very high in metal oxides, such as heavy iron glazes, as a possible problem.

Uneven thickness matters too. Digitalfire notes that thick and thin areas heat at different rates, which can lead to cracks.

Oven, freezer and thermal shock

Thermal shock happens when one part of a piece expands or contracts much faster than another. Mud Australia's examples are freezer to oven and oven to cold bench. Its advice:

• put cold items on a wire rack when placing them in a hot oven;
• set very hot items down on wood or cloth;
• never put porcelain directly on a stovetop or open flame.

Wedgwood says its stoneware and porcelain are oven safe up to 100 °C and to avoid direct flame and sudden temperature changes. Bone china is not oven safe unless specifically labelled. Mud Australia says its porcelain is oven safe but gives no maximum temperature, so ask your maker for a figure.

Digitalfire adds that heating from one side, as with a flame, creates large differences between the hot and cold sides, and that a crack from repeated shocks may be silent: the only sign can be a dull sound when the piece is tapped.

Crazing

Crazing is a network of fine cracks in the glaze. Digitalfire explains that it comes from a mismatch: the glaze expands and contracts more than the clay body. A piece can look fine from the kiln and craze later, especially after repeated sudden temperature changes such as cold liquids in a warm mug.

Digitalfire treats crazing on functional ware as a defect, and says crackle glazes, which craze on purpose, are not suitable for functional ware. Crazed glaze lets water reach the clay, which matters for microwave heating and hygiene. If a piece you use for food starts to craze, tell the maker. It may be a glaze fit problem across a batch.

Unglazed bases, scratches and stains

Many handmade pieces have an unglazed foot or base, and that bare clay is rougher than glaze. Mud Australia notes that stacking can leave small scratches where the bisque surface of one piece rubs the glazed inside of another, and recommends plate racks, felt or linen between pieces, with felt for darker colours. Wedgwood gives the same advice for stoneware and porcelain.

For tea stains and baked-on marks, Mud Australia suggests a magic sponge lightly moistened with water. Wedgwood recommends a soft, non-abrasive cleaner. Avoid scouring pads on gold, which Mayco warns can wear thin decoration away.

Chips, cracks and when to retire a piece

Mud Australia says small chips on rims can be smoothed with fine sandpaper by hand, on the matte side only and never the glazed side. If you are unsure whether a chipped piece is still safe for the microwave, oven or dishwasher, it asks you to contact them. Badly damaged or cracked pieces should be discarded, or repaired as decorative objects only.

A reasonable rule for any handmade tableware:

• Small rim chip on a dense body: smooth it or ask the maker, and keep it out of the microwave if the bare clay is exposed.
• Crack you can feel or hear: take it out of food use.
• Crazing on a food surface: stop using it for food and ask the maker.
• Broken piece you love: see our guide to repairing broken ceramics and glass.

Keep the care card with the piece

Care advice only helps if you can find it later. If the maker gave you a card, keep it with the receipt. If not, a short note of the maker, the clay body and any "hand wash only" or "not for microwave" instructions will save guesswork in a few years. Makers can use our guide to care cards for handmade objects.

Sources

• Product care, Mud Australia: dishwasher loading, wire racks in hot oven, hot items on wood or cloth, thermal shock examples, felt and linen, magic sponge, sanding chips on matte side
• Caring for your ceramic pieces, Mud Australia: microwave, oven and dishwasher statements, no stovetop or flame, discarding damaged pieces
• Your dinnerware care guide, Mud Australia: bisque surface scratching glaze, sudden temperature changes
• Care guide, Wedgwood: metallic decoration not microwave safe, gentle dishwasher cycle, bone china only if marked, oven safe to 100 °C, avoid flame and sudden changes, liners between stacked pieces
• Care for your wares, Feldspar: bone china dishwasher safe to 60 °C, liquid or gel detergent, gold hand wash only, real gold
• Overglazes, Mayco: gold overglaze not for microwave, avoid hard scrubbing
• Schedule B, chapter 69 (ceramic products), statistical notes, US Census Bureau: water absorption lines for porcelain and china (0.5%), stoneware (3%) and earthenware (over 3%), ASTM C373 test
• Microwave safe, Digitalfire: water absorption, unglazed foot, 1% porosity margin, 30-second test, metal oxides, uneven thickness
• Thermal shock, Digitalfire: bodies compared, one-sided heating, silent cracks
• Glaze crazing, Digitalfire: cause, delayed crazing, defect on functional ware, crackle glazes
• Earthenware, Digitalfire: porosity of earthenware, flame test comparison
• Stoneware, Digitalfire: semi-vitreous, brittleness and thermal shock
• FAQ, Leach Pottery: Standard Ware is stoneware with a small amount of iron