Estes Skylab #001973, Build, Part 22, Reduction Adapter Bordering & Mask

On the transition, 

I started with faint pencil lines at a 1/8" from the bottom of the adapter cover.

Using my credit card straight edge, just the high ribs of the corrugations got black ink marks.   

The low spots on the corrugations were filled in, up to the black marks from the last step.

Keep referring back to the instructions and double check the quarter turn pictures.

All the white areas were covered with brown masking tape.

Notice how the tape is set over the black ink borders, down the midpoint of the black border line.

It is very important to spray directly over the open areas - not from the side.

The purpose of the black borders is to get a sharp outline - something difficult to do over all the corrugations.