My darkcloth is black Goretex, so I just suspend it above my darkroom sink and hose it off.
I was given a darkclothe that rode in the back of a van that was driven only on gravel roads. The photograher who gave it to me figured it had been loose in the back for a very long time as they have been digital since the Kodak DSLRs. I washed it in the washing machine I think or else in the bathtub but it needed it. It was grey on both sides and was not supposed to be and to top it off it was a large one so lots of dust.
I did notice the age of the thread but:
But really I didn't realize how badly it sucked, in my view, until I got the BTZS. Spendy for what it is, but well worth it.
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Most blest is he who lives free and bold
and nurses never a grief,
for the fearful man is dismayed by aught,
and the mean one mourns over giving.
- Hávamál verse 48
I have a few. One of is more than 30 years old and I have never washed one. I occasionally hang them in the sun for a few hours to air out and that keeps them fresh.
Hand wash, line dry.
Real cameras are measured in inches...
Mine is a dark bath towel. If it gets dirty it will go in the wash.
I would just hand wash and drip dry.
My dark cloth is double sided black velvet which I sometimes double as a still life background. However now Im shooting more on location it traps the heat. Good for shooting in the cold... not so good in the heat.
Well since i made mine from moleskin fabric (yes, i am a) cheap, b) lazy c) like it) - i just throw mine in laundry with black t-shirts..
Not that this is the recommended procedure, but a gentle wash with a cup of lemon juice will salvage fishy-smelling rain gear and Polypro, at least until you sweat in them again.