Frits and glazes are tested for chemical composition, particle size, thermal expansion and melting behaviour. The final test is always a firing trial on the buyer's own body, in the buyer's own kiln cycle.
Unlike floor tiles, frits have no single product standard with pass or fail values. The buyer and seller agree a specification, and the tests check each lot against it.
Laboratory tests
- Chemical analysis, often by X-ray fluorescence, shows the oxides in the frit. It confirms the recipe and can report lead and cadmium if you need proof that a frit is lead-free.
- Particle size, as residue on a named sieve or a particle size distribution, matters for milling time and glaze behaviour.
- Moisture content checks that the material stayed dry.
- Thermal expansion is measured with a dilatometer, a method set out in ASTM C372. It shows whether the frit will fit the body or risk crazing.
- Softening and melting behaviour is measured with a heating microscope or a dilatometer. It shows at what temperature the frit starts to soften and flow.
- Flow tests compare how far a melted sample runs on a slope against a reference sample.
Tests on liquid glazes
Ready glaze slurries have extra checks, because they are applied as a liquid on the line.
- Density, usually given in grams per litre, which controls how much glaze lands on the tile.
- Viscosity, which controls how the glaze flows and levels.
- Sieve residue, which shows whether the glaze was milled finely enough.
- Shelf life and settling behaviour, which matter for storage after delivery.
The firing trial
No data sheet replaces a trial. The end user applies the glaze to its own body, fires it in its own kiln cycle and checks the result against a reference.
Look at gloss, colour, opacity and surface quality. Common defects are pinholes, crawling, where the glaze pulls back from the body, and blisters. For sanitaryware, see crazing and pinholes in sanitaryware glaze.
For tiles, finished-tile tests show whether the glaze does its job. ISO 10545-11 tests crazing resistance of glazed tiles, ISO 10545-13 chemical resistance and ISO 10545-14 stain resistance. See what tests to order for tiles before shipment.
Food contact
If the glaze is for tableware or kitchenware, lead and cadmium release becomes a legal issue in many markets. ISO 6486 sets the test method for release from ceramic ware in contact with food. Limits are set by each country's rules, so check yours.
How to use tests when buying
- Approve a reference sample after a successful trial, and keep part of it sealed.
- Write the specification with target values and tolerances for each test.
- Ask for a certificate of analysis for every lot.
- Have an independent lab check a sample drawn at loading, and compare it with the reference.
- Ask the maker to tell you in advance if it changes a raw material or recipe.
Next step
We draw samples at loading and send them to an accredited lab. For the background on the product, see what ceramic frit is. To set this up for your order, book a free sourcing review.