There is an FYI that is on Reddit that addresses the safety of different materials. It also talks to the issue of material safety . There is something called the Material Safety Data Sheet (MSDS) that suppliers have to provide. Just google that and the material you are interested in and you can have fun for hours!
So to make Stainless Steel you need to have a small amount of chromium in there & that's why Stainless does not rust. But a lot of stainless steel is used in medical devices in general. So most stainless is considered safe. Similar for Brass, most brass musical instruments have used brass mouthpieces for centuries but people think that since lead is part of its alloy it is unsafe. Brass is used widely in plumbing world wide too. When you hear about lead pipes in drinking water its not the lead in brass that is the concern.
The thing you don't want to do is worry if you read something about toxic fumes at like 800 or 900 degrees for some material and worry about that, The internal temperatures in a Vaporizer doesn't come close to that.
I also think it is worth considering that so -called "safe" materials is put together with smoking in mind and somehow thinking the material might off gas or react with the smoke. When we are vaping materials we are not seeing temperatures anything close to when combusting. What we see manufacturers use in the chamber where vaporization occurs is glass, stainless steel, ceramic, aluminum and of course Gold (Nectar Hex). and if vapor comes into contact with something it is very sticky and not likely to adulterate the whole rest of the vapor produced.
