Back when I first started making pots I would work with ash glazes until my fingers were red, split and sore from the caustic nature of the material, same goes with iron glazes in which my hands and forearms were covered in a rash from the glaze. Within a short time all that folly came to an abrupt halt as I delved into the nature of the materials I was using and how to properly work with them and insure my safety and the safety of the potential user. Since I started making pots a number of materials have been reclassified and their safety questioned and guidelines established for percentage of use in glazes for these materials as well as creating a eutectic where the glaze melt is met and all the materials are in suspension, trapped within a solid. There are exceptions to what materials I will use and among those I will not and never have gone near are materials like various leads, uranium and several others but the most important thing about making pots is understanding the risk, reward and safety of what you work with. I always come from the viewpoint that ever material I use has some potential risk from the inhalation of particulate matter to heavy metal oxides that are best not absorbed by the body.
I assumed it went without saying that before you try anything, especially that you read off of a blog or a random page with a glaze formula that you investigate the nature of each constituent and understand how to properly handle the material. Since way back in my Old West approach to making and testing glazes, I have created a series of steps that are meant to ensure my safety and (yours) the user of my pots including not using materials that are deemed harmful on the food contact surfaces of pots, casting aside certain materials where the jury is still out on their safety and for myself, I always use an approved respirator, never a paper mask and wear latex gloves and sleeve protectors when using glazes that are not friendly in their liquid state (manganese and iron glazes spring to mind). All this being said, the bulk of my glazes/slips are made using pretty innocuous stuff like ball clay, feldspar, kaolin, whiting, neph sy, red art and gerstley borate with the additions of iron oxide, copper and cobalt. It is always best to err on the side of caution to keep you and your customers 100% safe and bear in mind, just because you read that someone else is willing to make use of specific materials doesn't mean that you should. Do your homework.
As another pottery observation, while looking at this stack of over a ton of materials isn't amazing that what ever you are ever looking for is inevitably at the bottom back of the pile. How does this always happen is it a law of physics?