Hello everyone, I have a question about the silver staining.

My friends tried to use SDS page and silver staining to detect the mucus from planarian. They used 12% gel and ran gel for 1.5 hours by using 80V and 120V.

After them, they used invitrogen SilverQuest Staining Kit to run silver staining, but the gel showed something wrong. The middle of the gel had a large transparent area such as this picture.

Although we search a lot of data, but there's no answer about this. Can someone help me understand the answer?

Thanks a lot.