Dear Mig,
Silver nitrate solution sloshed out of my dipper tank the last time I was making wetplate collodion photographs in my backyard and by the time I noticed I had dripped a trail of photosensitive heavy metal solution down the cellar stairs, across the big room in the cellar into my workshop, which exposure to ultraviolet light was rapidly turning black. What should I do?
Sincerely, Photosensitive Heavy Metal Solution Stainer Dude

Dear PHMSSD,
Easy peasy. Take some sodium thiosulfate fixer solution, wet a paper towel and use that to wipe it up. Wear gloves, because I think I remember hearing it’s carcinogenic. Works like magic on tiles. Pets and carpet, not so much I figure. Under no circumstances use cyanide fixer, because that contains cyanide and will kill you. And safety goggles, because silver nitrate in the eyes will blind you. And remember this is time-sensitive: you must get it all cleaned up before your wife notices, or she will ask you to finally get all these funky chemicals out of the house and into storage somewhere with better fire insurance.
Regards, Mig