Post #33269 by Saint-Thomas on Wed, May 7, 2003 8:08 AM

That's strange, it looks very pink in this context, but it was more of a crimson color in my photo editor....

Here's the deal on red. The colors red, orange, and yellow all depend on compounds which are normally very toxic and/or unstable. Things like Cadmium, Chromium, Uranium, Cupric Oxide (copper)just to name a few. However, that doesn't mean that your browns and greens are safe. Here's a MSDS quote for Manganese which is frequently used for rich, chocolaty browns:
"....adversely affect central nervous system with symptoms including languor,..., weakness, emotional disturbances,...,and paralysis."
It sounds pretty bad, right? But in a glaze, it should be safe. Why? Because glazes are made of glass. Proffessionals spend huge amounts of time testing, formulating, and testing again their glazes to assure that they are fully melted and as resistent to leaching as possible. However, Not all you buy follows the same self-imposed guidelines that some of us potters follow.
Try this experiment: Go buy a cheap green or blue plate at you local thrift store or Wal-Mart. Place a slice of lemon on it over night and see if the color changes. That color change is copper or cobalt coming out of the glaze and going into your body.

I'll get to the point about reds... at earthenware temperatures reds are no big deal. However, these same formulae don't work at a temperature where the clay will vitrify (ie. become waterproof.) A ceramist's options become more limited at this stage and generally more expensive. I personally know of a few ways to get a safe deep red, but can't afford it, so I have been satisfied for the time being with crimsons and pinks.

On a similar note, anything metallic looking is definitely NOT safe!!! There is way too much metal in that glaze and you will end up drinking it. The only exception is Gold which is likely real gold (Au) but you are still drinking it!!

Sorry for the long post. Anyone who wants to know more can email me. I love this stuff!