I cut a strip of acetate, not a very sturdy one, I would suggest a thicker one, but hey...I scribbled on different colors or marker and then spritzed it with alcohol, so the colors would move and mingle and create a watercolor effect. Heat set it a bit and then let it air dry.
So I cut the front of the card base to accommodate the "window"and then cut the same for the inside, but from thinner card. This way you won't see any red sticky tape and or how it was assembled.
For the sentiment I used Simon Says Stamps painted thanks die. I cut it from black card with Stick it on the back so it becomes a sticker and applied it above the "window".
This time I used a thicker acetate, we call it mica, but that wasn't as heat resistant as the "floppy"one, which I believe is overhead projector film, it was given to me, but as those machines tend to heat up I thinkit's made more heat proof.
Shame, as my panel warped, but I will weight it down under some books and see if it straightens....I'm thinking no, but we'll see.
It all adds to the handmade feel ;-) haha.