Safe mixing and ventilation

The main hazard: dust

The main long-term hazard in glaze work is dust, above all respirable crystalline silica: particles of quartz or cristobalite (crystal forms of silica) small enough to reach deep into the lungs. Crystalline silica can make up about 10 to 60% of a glaze's dry weight, and most clays (except kaolin) and many feldspars also carry fine quartz. The UK's Health and Safety Executive (HSE) says this dust "is very fine and invisible under normal lighting", so a room that looks clean is not proof that the air is.

Breathed in over time, it can cause silicosis, a lung disease that HSE describes as "serious and irreversible" and able to "cause permanent disablement and early death". It can also cause COPD (chronic obstructive pulmonary disease: long-term bronchitis and emphysema), which smoking makes worse. IARC, the World Health Organization's cancer agency, places inhaled crystalline silica in Group 1, "carcinogenic to humans".

Silica does not turn into fumes in the kiln, and a wet glaze is not an inhalation hazard unless it is sprayed: spray mist carries silica and dries to dust (see Spraying, below). The times to take care are when material is dry: opening bags, weighing, stirring powder into water, and cleaning up drips, overspray and slop once they have dried back into dust.

Exposure limits

Workplace rules set an exposure limit: the most silica a worker may breathe, averaged over an 8-hour day, in milligrams (mg) or micrograms (µg, thousandths of a milligram) per cubic meter of air.

Some pages quote 0.025 mg/m³ for Australia, but the official limit is still 0.05. Either way, the advice is the same: keep dust as low as you can.

Several EU member states set lower limits than the EU's. The limit where you live, the law that sets it and the national body for safety at work:

These are workplace limits. They bind employers, so no one inspects a potter working alone at home, though community studios and schools with staff are usually covered (check your local rules). The dust is the same at home, and the limits show the scale of the hazard: 25 to 100 millionths of a gram in each cubic meter of air, averaged over a day.

Almost no one has measured dust in hobby studios, so we suggest treating every dry-powder task as a dusty one.

Habits that matter most

Most protection comes from habits, not equipment. HSE's advice for potteries starts with avoiding powder and works down from there.

Avoid the powder where you can

• Buy ready-mixed glaze when it suits your work. HSE's first suggestion is "Buy in glaze ready for use, when possible", or a granular or slurry form.
• Choose safer recipes. HSE suggests "glazes that contain less crystalline silica". Digitalfire suggests a frit (factory-made glass ground to powder, which dissolves far less than raw materials) in place of raw barium carbonate, and a stain (a manufactured ceramic color) in place of large amounts of manganese, cobalt or nickel for blacks.

When you do use powder

• Scoop gently. HSE says to "Tip/scoop gently from bags" and to avoid large, deep containers, so the dust has less far to fall.
• Keep lids on whenever a container is not in use, including between the scale and the bucket.
• Work out of drafts. Weigh away from doors, windows and walkways, and keep other people out of the room.
• Add powder to water. We suggest putting the water in the bucket first and adding powder gently, rather than pouring water onto a dry heap. This is common practice, not a rule from the sources.
• Stir with a stirrer, not your hands, and wear gloves.
• Keep it wet. Clean up wet spills "so they do not dry out", and keep wet scraps in sealed containers.
• Mind the bags. Sacks carry dust on the outside. Roll empty ones up gently and bag them before throwing them away.
• Store powders covered, off the floor and away from where people walk.

A sensible order of preference

1. Buy ready-mixed wet glaze, and skip the powder.
2. Mix from powder under a ventilated hood, or outdoors in still air away from other people; wear a respirator in either case.
3. Indoors without a hood: a respirator, gentle scooping, lids on, and wet cleanup straight away.

This order is our suggestion, built on HSE's principle of avoiding powder first. For weighing and mixing step by step, see How to make a glaze.

Respirators

A respirator is a mask certified to filter fine particles from the air you breathe. It works only when it seals to your face, and it backs up good habits rather than replacing them.

Classes by region

The higher class filters a larger share of fine particles. Sources disagree on what an Australian P3 filters (at least 99%, or at least 99.95%), so buy the certified class sold in your region. A reusable half mask (covering the nose and mouth, with replaceable filters) fitted with P100 filters (P3 outside the US) is a common studio choice.

Fit and seal

A mask that leaks lets dust in around its edges, whatever its class. HSE warns that stubble and beards "make it impossible to get a good seal".

• Shave shortly before you work. Guidance differs on how recent "clean-shaven" must be. A UK maker, citing HSE, says shaved within 8 hours of starting work. The Australian and New Zealand fit-test standard asks for a shave before a fit test, "preferably within 12 hours". Shaving shortly before you work meets both.
• If you keep a beard, a loose-fitting powered respirator (PAPR: a hood or helmet with a fan that supplies filtered air) needs no face seal.
• Get the size right. Poor fit is a major cause of leaks. Workplaces use a fit test, a check that a particular mask seals on a particular face. At home, we suggest following the maker's instructions for checking the seal each time you put it on.

In our view, fit matters more than class: a well-fitted N95, FFP2 or P2 will usually do better than a loose P100.

When to wear one

HSE says a respirator is "normally not needed" where weighing and mixing happen in a ventilated enclosure, but "may be needed for maintenance and cleaning". Most home studios have no enclosure, so we suggest wearing one (N95, FFP2 or P2 at least; P100, FFP3 or P3 is better) whenever you:

• open bags or tip out powder;
• weigh powders and stir them into water;
• scrape, sand or grind dried glaze or bisque;
• do any dry cleanup, or empty a vacuum;
• spray glaze (in a booth: see below).

What is not a respirator

• Surgical masks, cloth masks and "nuisance dust" masks without a NIOSH, EN 149 or AS/NZS 1716 marking. We would not rely on them for glaze dust.
• A dust respirator "will not protect you against gases, vapors" (OSHA), so it does nothing for kiln fumes.
• Look after yours: OSHA notes that a dirty or misused respirator "can become a hazard". Store it clean, away from dusty work clothes.

Cleaning, clothes and hands

Dust that settles on floors, benches and clothes goes back into the air every time it is disturbed. After gentle handling, cleaning wet is the most useful habit you can have.

Clean wet

• Mop and wipe with water. The University of Utah recommends wet mopping floors and work surfaces daily, and HSE asks workplaces to wash down at the end of each day. At home, we suggest wiping and mopping after every mixing session.
• Never dry sweep, dry brush or use compressed air. OSHA bars these where they add to exposure, and HSE says never to brush or blow dust off skin or clothing.
• Vacuum only with a machine built for fine hazardous dust: HEPA in the US (a filter that catches at least 99.97% of particles 0.3 µm across), or at least dust Class M in the UK and EU. Elsewhere, look for an equivalent rating. Ordinary shop and household vacuums are not rated this way, and we would not use them, since fine dust may pass through and out of the exhaust. Wear your respirator to empty one.

Clothes, food and hands

• Wear studio-only clothes of a closely woven fabric that does not trap dust, and wash them often (Utah suggests weekly), apart from other laundry. HSE notes that dusty clothing keeps exposing you after the work is done, so we suggest changing before you go into the rest of the house.
• No eating, drinking or smoking in the studio. As Digitalfire puts it, "one should not confuse barium carbonate with table sugar when preparing coffee". Label every container.
• Wash your hands before eating, drinking, smoking or using the toilet, and clean under your nails. Use warm water and mild soap rather than an abrasive cleaner.

For keeping dust and materials away from children and pets, see Don't poison your family.

Local exhaust and spraying

Local exhaust

Local exhaust ventilation (LEV) catches dust where it is made: a hood or enclosure over the work, with a fan that draws air away from your face and out of the building. Weighing is where most of the dust is made, so HSE describes an enclosed weighing station with a small open front, and Digitalfire a slotted hood above the scale. If you have one, HSE's workplace advice applies:

• keep it away from doors, windows and walkways, because drafts defeat it;
• let in clean make-up air (fresh air that replaces what the fan removes, through a door gap, window or inlet);
• send the exhaust outdoors, away from doors, windows and air intakes;
• check that it is on and working before you start.

No source gives airflow figures for a hobby hood. Without a hood, rely on gentle handling, a respirator and wet cleanup.

Spraying

HSE warns that spraying "can produce mists containing RCS" (respirable crystalline silica), and that "glaze mists dry out swiftly and turn to dust". Every source we found says to spray only inside a ventilated booth.

• HSE wants an extracted enclosure and, "where possible, a water-backed booth", which catches overspray in water.
• Use a turntable in the booth, wear nitrile gloves and a respirator, and clean the booth and its filter before overspray dries.
• Dusting bisque with a brush before glazing makes dust too; we suggest a damp sponge instead.

Venting the kiln

What a firing gives off

Every firing releases fumes, even with plain clay. Water and carbon dioxide come off, with "a little carbon monoxide" from burning organic matter, and Dave Finkelnburg, writing in Ceramics Monthly, calls the potential for carbon monoxide "the most immediate hazard". Carbon monoxide (CO) is a gas that starves the body of oxygen, causing fatigue, headache and dizziness. Sulfur in ball and stoneware clays gives bisque firings their rotten-egg smell, and sulfur fumes burn the eyes, nose and lungs.

Glaze materials add more. Some metal oxides form fumes, "notably copper, zinc, manganese", which can cause metal fume fever, an illness with chills and fever. Lead "vaporizes at lower temperatures", and fluorspar, cryolite and lepidolite give off fluorine compounds. No one has published measurements from hobby kilns, so we suggest venting every firing.

Downdraft vents

A downdraft vent is a small fan unit fitted to the kiln. It draws a little air out of the firing chamber, dilutes it with room air and ducts it outdoors, catching fumes before they reach the room. Kiln maker Skutt says all kiln makers recommend one.

• It needs make-up air. Skutt's EnviroVent 2 sends 140 cubic feet (about 4 m³) of air outdoors each minute, and as much must come back in.
• It removes "hazardous fumes only, not heat" (Skutt), and should run independently of the building's heating and cooling.
• Duct it outdoors, away from windows, doors and air intakes. Finkelnburg recommends a squirrel-cage (centrifugal) fan, not a propeller fan.
• Some local codes require a kiln vent, so check yours.

A hood vent (a canopy over the kiln) is the alternative. It pulls in fumes that escape along with a lot of room air, but draws nothing from inside the kiln, and it also needs make-up air.

Where to put the kiln

• We suggest a garage, shed or room set aside for the kiln rather than a living space, and one you can close off from children and pets, as Skutt advises.
• Clearances. Sources differ: Skutt specifies at least 18 in (46 cm) from any wall or combustible material (anything that can burn), while CIRMA, a Connecticut insurer, suggests 3 ft (0.9 m) from anything combustible. Follow your kiln's manual; without one, keep 18 in from walls and 3 ft from anything that can burn.
• Floor. Use a non-combustible floor such as concrete or ceramic tile, never wood, carpet or vinyl. Keep lumber, paper and solvents away from the kiln.
• Electrics. CIRMA recommends a dedicated circuit, no extension cords or surge protectors, unplugging between firings, and a fire extinguisher within 25 ft (7.6 m).
• Room heat. Skutt says to keep the room below 38 °C (100 °F), or the controller may shut the kiln off. As the vent removes no heat, a small room may need a fan as well. Keep sprinkler heads and heat sensors from sitting directly above the kiln.
• Carbon monoxide alarm. We found no rule requiring one for an electric kiln, but burning organics make CO, so an alarm in the kiln room and the rooms next to it is a sensible, cheap step (see Don't poison your family).

Raku makes large amounts of smoke and CO; Utah advises doing it outdoors, away from air intakes and windows. For firing itself, see Firing a basic kiln.

Materials that need most care

Most glaze materials, including silica, clays, feldspars and frits, are mainly a dust hazard, which the habits above control. A shorter list is toxic in its own right, by breathing, swallowing or skin contact. Digitalfire adds that stains are generally much safer than raw oxides, and that "unbalanced glazes that release toxic metals can be made from any materials": food safety depends on the whole recipe, not on one ingredient.

An IARC group is a cancer classification: Group 1 means "carcinogenic to humans", Group 2A "probably carcinogenic to humans", Group 2B "possibly carcinogenic to humans", and Group 3 "not classifiable as to its carcinogenicity to humans", which means too little evidence to judge either way.

Borax, boric acid, soda ash and potash dissolve in water, so we treat them as the likeliest to be absorbed through broken skin or swallowed from unwashed hands.

If a recipe calls for raw barium carbonate, a lot of manganese, or any lead or cadmium material, look for a version that uses a frit or a stain instead. Glazecalc can compare the chemistry of the original and the swap; then test the new glaze.

Gloves, skin and eyes

Skin

• Wear gloves for wet or dry glaze; Utah says they "must be worn". HSE names nitrile for spraying. No source compared glove materials, so we suggest nitrile for all glaze work.
• Barrier creams are not gloves. HSE: "'Barrier creams' are not 'liquid gloves'".
• Silica dust and wet work both cause contact dermatitis (red, sore, cracked skin), and cracked skin lets materials in. Wash with warm water and mild soap, and use an after-work cream.
• Cover cuts. Barium compounds, for example, are not thought to pass through intact skin, but can through broken skin.

Eyes

• Wear safety glasses when grinding glazed pieces. We also suggest them when tipping powders.
• Looking into a hot kiln. Kilns give off infrared radiation (heat you cannot see) that "may cause cataracts". Recommended shades of IR-rated glasses differ: 1.7 to 3.0 (University of Utah) and 2.0 to 5.0 (University of Calgary). Shade 3 falls within both; go darker if spots appear in your vision.

Reading a safety data sheet

A safety data sheet (SDS; older ones say MSDS) is the supplier's document on a product's contents, hazards and handling. Every raw material and commercial glaze should have one; look on the product page or ask the supplier. It has 16 sections, and two matter most:

• Section 2, Hazard identification: the classification, a signal word such as "Danger", pictograms (small warning symbols) and hazard statements.
• Section 8, Exposure controls and personal protection: exposure limits, the engineering controls needed (ventilation and extraction) and the protective equipment to wear.

Pictograms and hazard statements come from the GHS (Globally Harmonized System), the international scheme for labeling chemicals. Borax, for example, carries the GHS08 health-hazard pictogram, the signal word "Danger" and the hazard statement H360FD, "may damage fertility; may damage the unborn child". As far as we know, SDSs in the UK, EU, Australia and New Zealand use the same 16 sections.

• Check the form of silica. HSE warns that crystalline silica "can be wrongly labelled as 'amorphous silica'".
• "Not classified" is not "harmless". A finished glaze with no pictograms still makes silica dust when dry.

This guide gathers published advice, but it is not a substitute for a material's safety data sheet, your kiln's manual or your local rules. Where they differ from what you read here, follow them.

Official guidance by region

These are the primary sources most worth reading. Most are written for workplaces, but their advice carries over well to a home studio.

• United States: OSHA's silica standard (29 CFR 1910.1053) and its advice for people who choose to wear a respirator; NIOSH's silicosis alert.
• United Kingdom: HSE's COSHH essentials sheets for ceramics (COSHH is the Control of Substances Hazardous to Health regulations), especially CR1 on preparing glazes and colors and CR5 on spraying them, and HSE's fit testing basics.
• European Union: Directive (EU) 2017/2398 sets the binding silica limit; each member state's own limit, and its national body for safety at work, are under Exposure limits, above. ECHA, the European Chemicals Agency, publishes classifications such as those for borates.
• Australia: Safe Work Australia's crystalline silica and silicosis pages.
• New Zealand: WorkSafe New Zealand sets the workplace exposure standards; MBIE's history of the silica standard gives the dates.
• Kilns: Skutt's kiln room guide, the Orton and CCSA sheet on kiln fumes, and above all your own kiln's manual.

Sources

• OSHA: 29 CFR 1910.1053, Respirable crystalline silica
• OSHA: 29 CFR 1910.134 Appendix D, Information for employees using respirators when not required
• OSHA: 29 CFR 1910.1200 Appendix D, Safety data sheets
• NIOSH: Silicosis alert (publication 92-107)
• HSE: COSHH essentials CR1, Glaze and colour preparation
• HSE: COSHH essentials CR5, Spraying glazes and colours
• HSE: Fit testing basics
• Safe Work Australia: Research on a lower workplace exposure standard for respirable crystalline silica
• Enviliance: Report 16612, Australia's June 2026 decision on the silica exposure standard
• MBIE (New Zealand): Work with engineered stone and materials containing crystalline silica, Annex III
• IARC: Monographs Volume 100C
• IARC: Volume 131, Cobalt, antimony compounds and weapons-grade tungsten alloy
• Science Media Centre Spain: IARC classifies talc (2024)
• ECHA: Risk Assessment Committee opinion on lithium carbonate, chloride and hydroxide (2021, PDF)
• PubChem: Cobalt carbonate, GHS classification, including its EU harmonised one
• ECHA: Risk Assessment Committee document on boric acid and borates
• Coslaw: EU introduces new CMR classifications under the 24th ATP to the CLP Regulation
• University of Utah EHS: Arts safety: ceramics
• University of Calgary: Ceramics health hazards
• Digitalfire: Toxicity
• Digitalfire: Kiln fumes
• Digitalfire: Barium and compounds toxicology
• Digitalfire: Manganese inorganic compounds toxicology
• JSP: What levels of protection do particulate filters provide?
• JSP: Why is a clean shave essential for a proper tight-fitting respirator seal?
• Skutt: Kiln room design and product specifications
• CIRMA: Kiln safety bulletin (2025)
• Ceramic Arts Network: Dave Finkelnburg, How and why to use a kiln vent
• CCSA and Orton: What is so bad about fumes?