Talc shortage? New Talc - Cim Talc and Fabi Talc

[Maggie M]

The tile is mainly used for kitchen backsplashes and in bathrooms. And yes, it is important for the glaze to be translucent. 

[Min]

If the new clay has been tested and is suitable for your tiles then I would be looking at adding either a small amount of a ceramic stain to the glaze or some copper carbonate. There are pro's and con's to both additions.

I looked up the SDS (safety data sheet) for this glaze and it doesn't give any hints on which is used.

Copper carb is prone to high amounts of gassing off which could leave pinholes or micro-bubbles in your glaze. I don't know how fluid your glaze is so this might or might not be an issue. If copper carb does induce this problem a change in firing schedule could alleviate it. 

A ceramic stain, probably from Mason Stains, is my other thought on what was used for the green colour in the glaze. Have a look at the Mason colour chart, find a stain you think is closest and purchase the smallest amount you can and try that.

Is your glaze is in liquid form when you purchase it? If so then you need some way of measuring the dry glaze. There are a couple ways to do this but the fastest is probably to weigh out some liquid glaze then dry it out then reweigh it. When you know X volume of wet glaze equals  Y weight of dry glaze try the copper carb at 1% and/or a stain at 1%. Fire those and then tinker with the amounts to fine tune the colour. (run the glaze through a 80 mesh sieve after adding the extra colourant)

If you purchase your glaze dry then easy peasy just add the extra colourant to a small test amount and try that.

[Ron Roy]

I heard that the American Talc Company (Texas) sold out because there were hundreds of their workers  suing over asbestos type disease. Some talcs have those needle like fibers that cause lung disease. Be aware that every talc has a different analysis and clays and glazes have to be adjusted to get the same results - RR

[Dick White]

Ron, that's interesting. We know that NTYAL was run out of business for that reason. Geologists tell us that talc deposits and asbestos deposits are sometimes close together and sloppy mining practices can result in asbestos contamination of the talc output. It was alleged that NYTAL was thus contaminated, though Vanderbilt (the company that owned the mine) denied it. The cost of litigation to prove their case was too much and so they cut their losses and shut the mine. The AMTAL mine in Texas was purportedly clean, and so it became a major North American source for our talc. Your sources are now suggesting it wasn't so clean after all. We do know from the business world that Daltile, the huge wall and floor tile producer headquartered in Dallas, TX, was a significant customer. A few years ago, Daltile bought the mine from AMTAL, supposedly to improve their vertical integration controlling everything from raw materials sources to sales, but at least they continued to service the rest of the AMTAL customer base (including us mere potters). However,  in 2021, Daltile reduced the customer list to exactly one, itself, and the North American ceramics world has been scrambling ever since.

So, what your sources are suggesting, it was not merely Daltile buying out one of its materials suppliers to improve its own profitability, but AMTAL was happy to sell its looming liabilities. Interesting.