[alt-photo] On working with hydrochloric acid

[Harlan Chapman]

A gentle warning on a sneaky little hazard in using hydrochloric acid
(muriatic acid):

The acidic component is a gas, hydrogen chloride (HCl). Even dilute
hydrochloric acid will liberate the gas into your working environment.
Within reason this doesn't present a serious toxicity hazard and with good
ventilation you will be fine - hydrochloric acid is surprisingly friendly
to work with considering it's strength. But nearly any metal (aluminum,
iron, copper, even most stainless steel alloys commonly used) in your
entire workspace, even across the room, will begin to corrode. The
corrosion will be slow, insidious and damaging. Once noticed you'll find it
everywhere. So don't work with HCl in a darkroom space that may include
valued metal objects like clocks, cameras, dry mount presses, cutters…
Don't use it in a stainless steel sink unless you know it is an
HCl-resistant alloy. And don't store concentrated (even dilute)
hydrochloric acid solutions inside unless double or triple packaged as even
the best sealed bottle will likely leak fumes slowly into your storage
space and destroy it.

Mix hydrochloric acid, use it, store it, and dry paper treated with it
freely outside.

The volatile corrosiveness of HCl largely is not shared with most other
acids commonly used in photographic/printing processes.  Oxalic, acetic,
citric, dilute sulfuric, and dilute nitric, are OK, they won't liberate
undetectable vapors that slowly chew on metals throughout your workspace.

Happy printing,

-Harlan