A Low Cost Tester of Glaze Melt Fluidity
A One-speed Lab or Studio Slurry Mixer
A Textbook Cone 6 Matte Glaze With Problems
Adjusting Glaze Expansion by Calculation to Solve Shivering
Alberta Slip, 20 Years of Substitution for Albany Slip
An Overview of Ceramic Stains
Are You in Control of Your Production Process?
Are Your Glazes Food Safe or are They Leachable?
Attack on Glass: Corrosion Attack Mechanisms
Ball Milling Glazes, Bodies, Engobes
Binders for Ceramic Bodies
Bringing Out the Big Guns in Craze Control: MgO (G1215U)
Ceramic Glazes Today
Ceramic Material Nomenclature
Ceramic Tile Clay Body Formulation
Changing Our View of Glazes
Chemistry vs. Matrix Blending to Create Glazes from Native Materials
Concentrate on One Good Glaze
Cone 6 Floating Blue Glaze Recipe
Copper Red Glazes
Crazing and Bacteria: Is There a Hazard?
Crazing in Stoneware Glazes: Treating the Causes, Not the Symptoms
Creating a Non-Glaze Ceramic Slip or Engobe
Creating Your Own Budget Glaze
Crystal Glazes: Understanding the Process and Materials
Deflocculants: A Detailed Overview
Demonstrating Glaze Fit Issues to Students
Diagnosing a Casting Problem at a Sanitaryware Plant
Duplicating Albany Slip
Duplicating AP Green Fireclay
Electric Hobby Kilns: What You Need to Know
Fighting the Glaze Dragon
Firing Clay Test Bars
Firing: What Happens to Ceramic Ware in a Firing Kiln
First You See It Then You Don't: Raku Glaze Stability
Formulating a Clear Glaze Compatible with Chrome-Tin Stains
Formulating a Porcelain
Formulating Ash and Native-Material Glazes
G1214M Cone 5-7 20x5 Glossy Base Glaze
G1214W Cone 6 Transparent Base Glaze
G1214Z Cone 6 Matte Base Glaze
G1916M Cone 06-04 Base Glaze
G1947U/G2571A Cone 10/10R Base Matte/Glossy Glazes
Getting the Glaze Color You Want: Working With Stains
Glaze and Body Pigments and Stains in the Ceramic Tile Industry
Glaze Chemistry Basics - Formula, Analysis, Mole%, Unity, LOI
Glaze chemistry using a frit of approximate analysis
Glaze Recipes: Formulate Your Own Instead
Glaze Types, Formulation and Application in the Tile Industry
Having Your Glaze Tested for Toxic Metal Release
High Gloss Glazes
How a Material Chemical Analysis is Done
How INSIGHT Deals With Unity, LOI and Formula Weight
How to Liner-Glaze a Mug
I've Always Done It This Way!
Inkjet Decoration of Ceramic Tiles
Interpreting Orton Cones
Is Your Fired Ware Safe?
Leaching Cone 6 Glaze Case Study
Limit Formulas and Target Formulas
Low Budget Testing of the Raw and Fired Properties of a Glaze
Low Fire White Talc Casting Body Recipe
Make Your Own Ball Mill Stand
Making a Plaster Table
Making Glaze Testing Cones
Monoporosa or Single Fired Wall Tiles
Organic Matter in Clays: Detailed Overview
Outdoor Weather Resistant Ceramics
Overview of Paper Clay
Painting Glazes Rather Than Dipping or Spraying
Particle Size Distribution of Ceramic Powders
Porcelain Tile, Vitrified or Granito Tile
Rationalizing Conflicting Opinions About Plasticity
Ravenscrag Slip is Born
Recylcing Scrap Clay
Reducing the Firing Temperature of a Glaze From Cone 10 to 6
Simple Physical Testing to Compare Clay Materials
Single Fire Glazing
Soluble Salts in Minerals: Detailed Overview
Some Keys to Dealing With Firing Cracks
Stoneware Casting Body Recipes
Substituting Cornwall Stone
Super-Refined Terra Sigillata
The Black Art of Drying Ceramics Without Cracks
The Chemistry, Physics and Manufacturing of Glaze Frits
The Effect of Glaze Fit on Fired Ware Strength
The Four Levels on Which to View Ceramic Glazes
The Majolica Earthenware Process
The Physics of Clay Bodies
The Potter's Prayer
The Right Chemistry for a Cone 6 MgO Matte
The Trials of Being the Only Technical Person in the Club
The Whining Stops Here: A Realistic Look at Clay Bodies
Those Unlabelled Bags and Buckets
Tiles and Mosaics for Potters
Toxicity of Firebricks Used in Ovens
Trafficking in Glaze Recipes
Understanding Ceramic Materials
Understanding Ceramic Oxides
Understanding Glaze Slurry Properties
Understanding the Deflocculation Process in Slip Casting
Understanding the Terra Cotta Slip Casting Recipes In North America
Understanding Thermal Expansion in Ceramic Glazes
Unwanted Crystallization in a Cone 6 Glaze
Using Plaster Bats
Variegating Glazes
Volcanic Ash
What Determines a Glaze's Firing Temperature?
What is a Mole, Checking Out the Mole
What is the Glaze Dragon?
Where Do I Start?
Why Textbook Glazes Are So Difficult

Having Your Glaze Tested for Toxic Metal Release

Description

Having Your Glaze Tested for Metal Release

Article

Labs do not test ceramic glazes for "food safeness"; they only determine how much of a given metal leaches out into water under standardized test conditions. It is your responsibility to ask them to check for the right the metal(s), evaluate the accuracy they claim, and determine what 'safe levels' are. In the absence of legal standards for "food safeness" for glazes (with the exception of lead and cadmium) we use drinking water standards (however there are no drinking water standards for all the materials used in ceramics). If you don't feel qualified to evaluate the results yourself, contact or search writings of an industrial toxicologist.

Certain things are obviously worth testing for and others not. If you are not using any materials that contain lead, there is no point in testing for this. The only possible sources are frits, and few suppliers would even have a leaded frit in their building. If your glaze contains barium or lithium, these would be worth testing for if you use a material that sources them. Raw metallic colorants like cobalt, manganese, chrome are a concern on food surfaces. The manufacturer will have information of the contents of any stains you use. While stains are blended compounds (to add stability) and are pre-fired at high temperatures and are supposedly more inert than raw colorants, there is still a potential for leaching.

On the list of labs at https://digitalfire.com/services/database.php?list=labs, the Brandywine Science Center specializes in this type of testing. Their page details how to prepare and send your sample.

For doing your own testing, please see the GLLE test, if you are doing nothing to test right now, these simple tests are an excellent start.

3M Lead Check kits can be bought at amazon.com. Search "home water test kit" for products that can sense a range of heavy metals.

Please read the linked articles. No single thing is more important than knowing more about the materials you use and how to make glazes that have a balanced chemistry (making them less likely to leach). Using a frit about whose chemistry you know nothing is asking for trouble. The best piece of advice is to do use a liner glaze (see link below). Your clay supplier should be able to recommend safe liner glazes (and accompanying firing schedules) for each of the bodies there sell.

Copper can destabilize a glaze and make it soluble

Copper can destabilize a glaze and make it soluble

A closeup of a glossy Cone 6 glaze having 4% added copper carbonate. The bottom section has leached in lemon juice after 24 hours. This photo has been adjusted to spread the color gamut to highlight the difference. The leached section is now matte.

Metal leaching from ceramic glazes: Lab report example

Metal leaching from ceramic glazes: Lab report example

This lab is certified by the US Department of Environmental Protection (DEP) for drinking water and waste water analysis. They also provide pottery glaze leaching analyses (the water is kept in contact with the glaze for many days then analysed for trace levels of specific metals). Each suspected metal must be tested for and each entails a separate charge ($30-60 in this case). That means that testing one glaze for several metals could cost $200. How to make sense of these numbers? Google the term: "heavy metals drinking water standards", and click "Images". You will find many charts with lots of data (some of them show multiple sources). By searching pages for this term you will find books having detailed sections on each of the metals. This can seem overwhelming, but typically you are only interested on one metal in a specific glaze (often cobalt or manganese).

Links

Articles Are Your Glazes Food Safe or are They Leachable?
Many potters do not think about leaching, but times are changing. What is the chemistry of stability? There are simple ways to check for leaching, and fix crazing.
Articles How to Liner-Glaze a Mug
A step-by-step process to put a liner glaze in a mug that meets in a perfect line with the outside glaze at the rim.
Articles Attack on Glass: Corrosion Attack Mechanisms
Max Richens outlines the various mechanisms by which acids and bases can dissolve glass and glazes. He provides some information on stabilizing glazes against attack.
Articles An Overview of Ceramic Stains
Understanding the advantages of disadvantages of stains vs. oxide colors is the key to choosing the best approach
Articles G1214Z Cone 6 Matte Base Glaze
This glaze was developed using the 1214W glossy as a starting point. This article overviews the types of matte glazes and rationalizes the method used to make this one.
Articles Is Your Fired Ware Safe?
Glazed ware can be a safety hazard to end users because it may leach metals into food and drink, it could harbor bacteria and it could flake of in knife-edged pieces.
Glossary Leaching
Ceramic glazes can leach heavy metals into food and drink. This subject is not complex, there are many things anyone can do to deal with this issue
Tests Glaze Leaching Test

By Tony Hansen


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