To use chalk well (whatever kind you use), you need a sharp edge and a *light* hand. To draw the apron edge, stand the chalk straight up and down with the long edge of the chalk (not the point) on the cloth. Stand behind the chalk (not to one side), and push the chalk straight away from you along the curve in one smooth movement. Swish! No little sketchy strokes. Keep the edge of the chalk parallel to the line you're drawing so that you don't wind up with a smeary line, and keep the chalk straight up and down. Think of it like an ice skate on ice.

"Sew True" company (http://sewtrue.com/) sells an excellent little tailors chalk sharpener. Go to their web site, and type "chalk sharpener" into the search box. They also sell Jems tailors chalk very cheaply. I love the chalk sharpener, and it has a little shavings catcher below the sharpening edge, so it doesn't get all over the place.

I work with dress tartans, too, and I still use white chalk. Well, that's not quite true - real tailors chalk is actually slightly gray, so the line actually shows up. Once I'm happy with the chalk line, I put a line of basting stitches to mark it, because I find that, on light tartan, the chalk *is* hard to see, and because the chalk rubs off easily. I ordered a box of the light yellow chalk once, thinking I'd need it for light tartans, but it leaves too colorful a line in my estimation, and I've found I don't really need it. So, it's sat on my shelf unused.

Anyway, real tailors chalk is a dream to work with compared to soap or blackboard chalk, and it's worth getting some. I like Jems the best. I can't get the triangular chalk that Robert talks about, but I've used it before, and it's great, too. And the chalk sharpener would work well on it as well.