thanks so much for sharing some of George's techniques with us! I love his work!! and would love to just watch him paint!
I use a razor blade when working with the oilies too. I like those little grippers that you can get to hold the straight edged blades because I've knicked my fingers a lot of times when not using one!
One thing you can do if you want a really straight edge in the painting is lightly scrape your oil pastel with the razor watching so that you get coverage down the length of the blade. Then slightly stand the blade on the area you want a very straight edge, press down and pull to the side. The paint will spread under the edge of the blade away from the line. (Hope that made sense....if you've ever done sheetrock mud, you'll be a pro