I used Bissell carpet and upholstery machine and solution to clean bench and buttons turned black. I assume that it’s rust caused by oxidation of metal
belpe the fabric. I’ve tried everything - salt and lemon, baking soda, vinegar, rust remover, laundry booster, and multiple stain removers to no avail. Rust hoes away and returns to ongoing oxidation. Can this be saved ?
This should help: http://www.howtocleanstuff.net/how-to-remove-rust-stains-from-upholstery/
Your best bet is to reupholster the headboard. It's a fairly simple project. You'll need fabric, scissors, a large needle, new buttons, and a staple gun. The first four items are available at a fabric store and the stapler from a hardware or home improvement store. It's also an item you'll use many times over the years so I'd recommend buying an electric one.
If you can take the buttons off, you can spray them with rustoleum spray. I had a friend that had a old singer sewing machine and her house flooded during a hurricane and the metal started rusting and she used the spray and it help.
You really have to replace the buttons. The button fabric is ruined.
you can try IRON OUT but if buttons are not treated theywill just rerust even from humidity in air, I agrre with Kelli replacing buttons is best easiest long term fix
Agree with others who have said that the buttons need to be replaced, as the coating on the present ones has deteriorated. Also agree that the fabric should be replaced. As the rust has already permeated the fabric fibres, it will likely continue to seep out, or down into the stuffing, with time.
Also, from the photo, it appears that the fabric has sustained water mark damage and possibly additional surface damage due to the extensive use of various cleaners.
If the visible black outlines are due to mildew beginning to invade the interior stuffing, this will need to be completely replaced with new before the new cover and hardware are installed.
I would replace or re- coat them. Cleaning it with any solution will only stain the rest of your headboard