Hey,
Hi to everyone first!
I had several bobbins, 15s, came with a sewing machine that had been left in the rain. All but one had thread on them, and all very rusty and full of thread. I decided I didn't want to toss the thread, as I could use it as test thread, so I submerged the bobbins in white vinegar, cheaper than evaporust. A few hours later I scrubbed with a tooth brush, bobbins thread and all, they came out very clean. The thread is still stained but useable. After the vinegar bath I rinsed them well and hung them up to dry. If the thread does break later, I can always toss it then!
Ethel