Glazes are labeled per ASTM D-4236 as follows:

AP Non-Toxic: 
Contains no ingredients considered to be unsafe by the ACMI, or contains such ingredients at low enough amounts to be considered safe.  May be used by any grade K-12.  Glazes which are AP Non-Toxic in wet form might not be in dry form or when sprayed.

CL Label: 
This means there is a Caution Label written on the jar.  This Caution Label could say a variety of things, and recommendations should be followed to ensure safety.  CL label product is not allowed in schools in grades K-6.

Lead: 
Certain states and most schools have special regulations relating to lead bearing products.  In 2009, most manufacturers phased out of leaded glazes to make it easier to comply with regulations.  We only have a few leaded glazes left, and very small quantities while supplies last.  These are all clearly marked on the website.  

Federal law requires the use of non-toxic products in grades K-6 and requires art materials labeling that confirms to the ASTM D-4236 Standard.  Under the Federal Hazardous Substances Act, children should not be permitted to use art material products labeled "not recommended for the use of children."  Products with this statement may not be sold in school systems in states with laws prohibiting the sale of such products to pre-kindergarten or grades 1-6.

Dinnerware Safe: 
To be labeled dinnerware safe, the glaze contains no lead or cadmium bearing ingredients.  However some glazes that do not contain lead or cadmium are still not recommended for surfaces which come in contact with food or drink due to the soft or crackle nature of the glazes, even though they pass tests for hazardous release.

In order for glazes labeled dinnerware safe to be dinnerware safe, they must be fired to recommended firing temperature. 

Tableware producers must have all finished ware tested and approved as sale for dinnerware through a certified laboratory due to possible variations in firing temperature and possible contamination.

It is impossible for any glaze manufacturer to guarantee the finished properties of its products, since application and firing are critical factors over which the supplier has no control.  Table producers are responsible for complying with FDA guidelines for lead release.  Any statements concerning dinnerware safety must be confirmed by the producer of the products through lead release testing by an approved laboratory.

None of these products should be taken internally.  They may contain ingredients not suitable for ingestion or inhalation

AMACO Product Encyclopedia and Glaze Safety Brochure