Bobbin thread black with ???

[Allison S.]

I'm working on a QOV quilt with a white backing..of course, right?....and I noticed that my granny smith apple green thread has areas that is black.  It's the bobbin thread only.  Before starting this quilt I removed and cleaned the bobbin, wiped out the bobbin case, and made sure everything was working great since EVERYTHING would show on the back of this quilt.  I didn't expect to have the problem I'm having, and not sure what's causing it. I'm NOT technical at all.  Cleaning the bobbin itself is about as techie as I get. 

It's not the entire thread.  It shows up randomly.

Any ideas on where the trouble is and what I can do about it?

[ffq-lar]

If everything else is clean, there are two thoughts. One--if you're using pre-wound bobbins, check the others in the pack for random black spots. Then yell at the manufacturer. Two-- If you wind your own, check the cone you wound them from. I place the cones I'm using at the back of the machine when I'm changing threads during quilting. When I stop for the day, those cones stay there when I move the head to the right to put her to bed. IF I push too far, or in the morning when I start again, I may slide the machine over a bit--- the track can hit the cone (right about the shoulder). Oxidation that builds up on the track can transfer to the thread in just a small area. (Yes, I clean the track as part of my daily routine, so the oxidation is from the day before and can transfer while I'm moving the head to oil, etc. Please don't think I'm a slob!) And, being in only one spot, the unwinding of the thread means you'll sew for a yard or two before the spot shows up again. It took me FOREVER to figure this out. Why was there a black spot on the thread? Grandma's Famous Spot Remover will cleanse the spot. Apply liberally but just to the spot, blot with a paper towel, and repeat until the spot is gone. You may also want to spot-clean the already-sewn spots, but it may make the spot migrate onto your white backer, so caution! Hoping this was helpful!