I wrote about nylon vs polyester sliders a few months ago and how polyester slides are impossible to dye. For this reason I have switched to stocking nylon sliders so my customers can dye to match their other notions. Plastic findings can be the most difficult to dye and sometimes you might give up on them too soon. Here’s a few tips on how I dyed the slides in this picture. I used RIT Lemon dye and they came out fairly true to shade. But they took longer to take up the dye and a little bit of special handling.
I’ve done a lot of testing with dying these sliders with acid and RIT dyes. They are 100% nylon plastic not nylon coated metal. The secret to getting the color that you want is acidity and time. I recommend dying all your notions as usual but once you’ve taken out your fabric, elastics, channeling and hook and eyes out of the dye bath add more acid (vinegar) to the dye bath. Increase the heat to a slow boil and continue to heat them until they are the shade you desire. It will probably take longer than you want it to. Adding extra dye to the bath at this point helps also. If using RIT sometimes adding salt can help encourage them to take up the dye.
By using this method I’ve been able to get all the white rings and sliders that I stock to dye evenly. I’ve switched to stocking only nylon rings and sliders for this reason. This is the method I’ve developed through trial and error and your mileage may vary