After working on a piece for a few hours I had a layer set over a sketch I did for darker lines, wanted it to be separate from said sketch. After exiting and coming back to it I realised that the layer had been dropped and lines had merged with the sketch and I don't want that to happen, is there a way to separate the lines from the sketch? I'm also using Corel Painter Essentials 6, any help or advice would be much appreciated.
I don't think so. To preserve your layers when saving Save as a .riff file. Otherwise the layers will collapse if saving as jpeg, png, etc.
If your background is a sketch on mostly white, this might work...
1. Select all (Ctrl/Cmd+A)
2. Copy (Ctrl/Cmd+C)
3. Paste (Ctrl/Cmd+V)
4. In the Layers panel (Window > Layers) select the new content you patested, and along the top of the layers panel is a little combobox that says "Default". Try changing that to "Gel". The sketch should now float. You can try different merge modes, or buildup a couple of layers of sketch if needed.
This is a work-around, so there may be some limitations but at least you can paint underneath your sketch!