Estes Great Goblin, #9724 Build, Part 21, Masking One Black Fin

On the model, there are three yellow fins and one black fin. 

Decals go on the yellow fins.

Plan ahead as to which fin will be painted black.

Looking at the kit box art, the launch lugs aren't seen. We can assume the lugs are on the back side of the body. 

That black fin is also towards the back.

Here's my old Goblin upscale showing the black fin and the lower launch lug.

Everybody has their own techniques for masking. I use Scotch tape marked with a Sharpie pen so it's easier to see.

On the left is how many builders mask off a fin with a rounded leading edge. Where the fin tip leading edge meets the body tube you'll see square corners. 

On the right I've added two small strips of tape starting to "round" the paint line around the leading edge.

More pieces of tape are added until I get a good half round edge. It looks like there is 12 pieces of tape over the half circle mask.

Here's how the back end is rounded off. I don't use as many pieces of tape on the back.

Note the masking tape around the inside edge of the body tube. The exposed motor mount is masked off with a rolled up paper towel pressed into the recess area.