Cutting the registration marks:
The final step in carving the key block is cutting the registration marks. There are two common ways to do this. The first method, used when none of the design elements come near the registration marks, is to simply slice a notch into the wood at the appropriate places. The corner, and one side, of the printing paper will simply slip into the two notches.
But if design elements happen to come near to the marks, you will find that the 'valley' that you carve around those areas comes right up to the registration marks. In that case, you will have to carve them to look something like this, with a little 'shelf' on which to place the printing paper.
Whichever method you end up using, don't dig them out too deeply. The small notch in the top illustration for example, doesn't have to be much deeper than the thickness of your printing paper. The farther down you dig, the more difficult it will be to accurately register the paper later.
Once the two marks are cut, take your block to the kitchen sink, and wash off the remains of the glued-on tracing under running water. If necessary, use a not-too-hard brush to lightly scrub off any bits that remain stuck to the wood. Don't worry about getting the block wet - during the printing process we are going to be rubbing wet pigment all over it anyway ...
When it is all clear, pat off the water and set it aside to dry off. It should look pretty good at this stage - enjoy it while you can, because we're soon going to be smearing pigment all over it, and it'll never look this clean again!