When they are completed I will cut them apart and work on the back side of each card individually. I will also put a wash on the front four corners to add a little more color.
To the right is a shot of the full sheet of watercolor paper (I use Fabriano 140 lb extra white block). The photos below are just closeups.
I ruled off my sheet for six invitations then found the center of each card and worked my sketch from the center marks. After all of the cards were drawn, I then used a light wash of Davy's Gray, Cobalt Blue and Purple Lake to go over my pencil marks. Then erased the pencil. This way the invitations come out clean and free of lead. I don't want pencil showing through the watercolor it looks unprofessional.
I have two important things to say about that. First if you look at paintings done by the watercolor masters you don't see any pencil marks from the underlying sketch. So that leads me to the conclusion that even the masters didn't want their sketch to show through their paintings. This also leads me to the conclusion that artists either couldn't cover up their sketch lines, or just chose not to bother and liked it, and the world of art has actually approved it.
I just thought it odd that somewhere along the line the rules changed and pencil was allowed to show, in fact, it is now considered an actual part of the art itself. My personal opinion about the matter is that if the masters could do a watercolor without their sketch lines showing through than so could I and I succeeded. Both processes work for the individual artist, that is the freedom of art!