Okay kiddo, have you ever seen a picture or a drawing that you really liked and you wanted to make a copy of it? Maybe you're not able to draw it yourself so you want to keep it or share it with someone else? Well, demountable copy is a way to do just that!
Sometimes, pictures or drawings are put on special paper that makes it easy to transfer the image onto another piece of paper. This paper is called the demountable copy paper.
When you want to make a copy of a picture or a drawing, you put the demountable copy paper on top of the original and lightly trace over the lines with a special pen. The pressure from the pen transfers the image onto the demountable copy paper.
Now you have two options, you can either keep the copy on the demountable copy paper (which is like really thin, transparent paper) or you can move it to another piece of paper. To do that, you can use something called a mounting sheet which is like a big sticker. You stick the demountable copy paper onto the mounting sheet and then you peel off the backing to reveal a sticky surface. Then you can place the mounting sheet onto another piece of paper and press down. The demountable copy paper will stick to the new piece of paper and you'll see the image you copied.
So there you have it, demountable copy is just a way to make a copy of a picture or drawing that you like using special paper that can transfer the image to another surface. Pretty cool, huh?