How to clean Hopsack?  

Awesome Orange
Hi
I talked to my vintage source. He says the best thing he has tried is a product called Awesome Orange which you can get at Walmart. His directions are to wet the whole fabric then gently work the stained area with a soft brush (toothbrush) or finger nail until it lifts the stain. Let air dry. I can't tell very well from the image but are you sure that is hopsak and not polyknit? Good Luck!

Hopsack is a weave, not a fib...
Hopsack is a weave, not a fiber. It can be woven of wool, polyester, acrylic, linen or any other fiber.
Wool doesn't hold on to most kinds of dirt and is usually pretty easy to clean. I have had good success with just regular dish detergent. I squirt some into a plastic container with a lid (like Tupperware or Rubbermaid), add a little water, and shake until the thing is filled with suds. Then rub the suds into the fabric with a damp sponge. Repeat until the stain is gone.
Rinse the detergent and dissolved dirt out with a clean sponge and clean water, blotting and rinsing the sponge until no more suds comes out of it.
Blot the upholstery with clean towels.
Quicker method: use more water and vacuum it out with a wet-vac.
Synthetics tend to hold on to oily stains and mild detergent may not be enough to get them out. You might need a naptha-based solvent (dry-cleaning fluid).

more Awesome than Awestome Orange
The best cleaner I've used on hopsack (whatever the fiber) is called Awesome (not to be confused with Awesome Orange). For some mysterious reason, it's sold almost exclusively at dollar stores. It's easily the most effective cleaner I've ever found. Even better, it's really cheap.
I used it several years ago to clean some hopsack covered Eames aluminum group chairs. The chairs were filthy with grease and stains. I sprayed them with Awesome, waited 20 minutes, and hit them with the pressure washer. When dry, they looked like new.

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