Thornton's Art Supply Liquid Chalk Markers

I have chalkboard wallpaper on my wall (which is basically black contact paper), and have used all sorts of chalk paint pens on my wall without issue. Some pens leave a very faint color stain, though hardly visible and doesn't bother me. I bought this set mainly for the gold color, and tried it this afternoon. The color was vibrant, but not as metallic as I'd like it to be. In the light, it looked very nice, but without it looked like a darker yellow. Maybe an hour or two later I tried to wipe off part of the writing, it was VERY difficult to remove the markings. Most of it wouldn't come off. I didn't have time to deal with it then, so I left it, and came back to it a couple more hours later. I used a warm wet towel, a sponge, surface cleaner, all to no avail. Finally I tried goo-gone with a lot of elbow grease, and finally got everything off. Definitely returning.