I have thought about this subject off and on---and I just thought about it last week actually….due to my punches. I realized last week that I have not used my punches in quite awhile and I was remembering how, when I had only maybe 4 punches, I was using them tons! but now when I have many many more….I haven't used them but once in a while.
Which is sad b/c I look at punches, not for just what they punch out, but what ELSE I could make the punches do---as in using them for "nibbling" and "fretting" (I think you called it, DAniel), etc. Thus, I thought MORE of a material (punches in this case) would increase creativity, but it doesn't seem like it at the moment. But I tend to go through phases: use mainly colored pencils on one card, the next will be stamps, the next die-cuts, etc.
I can definitely see how the limited materials in a kit challenge could increase creativity…if you only have so much of a ribbon that was sent, then you really have to think on how to use it to make the most of it. (thus, it can also cause a "I only have one shot at this, since I have no more" anxiety too...
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I have done the "open layer" before---especially with some of the kraft paper I have---but I also have been afraid to do the "open layer" on cards I give away to people.
On a different note, I do enjoy "repurposing" things---even in crafting …I mainly repurpose items as tools with crafting ---- so for example, I won't throw away excess CS from a cut-out b/c I know I can use it to wipe up the glue I am going to use on the card in a moment after glueing it down. Since I only have limited napkins on hand right now, I get creative on using other stuff to act in-the-place-of. There are more things I do this "repurposing" with in terms of crafting, but none come to mind right now. I do know I repurpose items to help conserve other crafting materials though.