Why do I have black spots in western blot?

1, may be the presence of insoluble particles in the blocking solution, if the milk is not dissolved and poured it on the membrane, will cause a lot of insoluble particles attached to the membrane, which will lead to black spots on the membrane when the luminescence. Therefore, after the milk is dissolved, it is best to stand still, and then gently suck the upper layer of milk for sealing, and after the closure is over, be sure to wash it three times before adding a resistance.  

2, it may be that there are bubbles or insoluble particles in the gel, or the gel is not sealed well, resulting in uneven gel. Care should be taken during dispensing, using a liquid free of impurities.  

Hope my advice is helpful!