Short answer is yes. The process produces fumes and uses a number of chemicals.
http://www.finishing.com/faqs/blackoxide.html
I have not used the hot process but re-finished a rifle using the cold process. Pictures are here :
http://www.ctshooting.com/modules.php?n ... pic&t=2478
It looked great when it was done a seemed durable enough but over time it went from a very dark grey(almost black) to a light grey. Every time I wipe it down I get some iron oxide on the rag. Not really an issue but not clean like other coatings.
One thing I learned is that the metal MUST be cleaner than you think. Stripping followed by glass beading with soap and water clean up is not enough. I ended up using a chemical metal prep and then had success with the black oxide.
I think if I do it again I would try the Duracoat process. In fact, if you are not wild about doing it yourself, Mike-Sid does that type of coating.
Bottom line is hot processes involve hazardous materials, require the correct equipment and need to be done very carefully to come out right.
"Those who make peaceful revolution impossible will make violent revolution inevitable." - John F. Kennedy 1962
NVPL :
http://www.nvpl.greatatlantictrophy.com/
WLOPA :
http://www.wlopa.com/index.htm