The only firearm finish I know of that is mostly hazard free is steam rust finishing. It uses water and heat… but will not give you a modern dark blue/black finish. You can get burned from steam, so it isn’t 100% safe.
All of the others use chemicals, some of which are very dangerous. Some, like cold bluing or hot water bath bluing are less dangerous but are still chemicals not intended for drinking, either straight or over ice! đŸ™‚
The MSDS safety sheets will actually tell you how dangerous each product is and exactly what kind of danger. They will tell you about skin contact risk, cancer risk, respiratory risks, environmental risks, etc. When I was in law enforcement, we had the MSDS data sheets on everything so we could mitigate risks and so that everyone was aware of any risk. We also had books on tanker markings so we didn’t die if there was a tanker crash with super bad stuff… we could read the tanker markings and know if we needed to stay away.
Nobody here can tell you if something is “safe” for you. Firearms are not “safe” and gunsmithing is not “safe” but neither is driving a car or eating fast food… all are things you need to read about and determine for yourself. Find the products and go to the manufacturers website and they will have MSDS data available for you.
Me personally, I hate caustic bluing… but Steve Sanders likes it and does it for other gunsmiths. So, Steve understands the risks, has proper ventilation and has the chemicals to neutralize and protect the environment (I know this because he and I have talked about it). He did his research.
