Sourdough Starter question

I started my first starter a week ago.  It has been bubbling so I've 'fed' it regularly but it has not doubled in size in 12 hours yet.  Today I moved it to a glass jar and I can now see through the side a growing layer of yellow-ish liquid in between the frothy top and the thicker layer below.  Is this a bad sign or a good sign?  Thanks.