It can be challenging to determine the iridised side of glass. The coating is very thin and so cannot be seen by looking at the edge. There are several ways of testing for the coated side. Two that I find useful are:
The pencil test – In this you put a pencil point or other point to the glass. You then look for the reflection at an acute angle to the glass. If there is a gap between the point and the apparent surface of the glass, the coating is on the other side. And in reverse, if the point is immediately reflected with no gap, the point is touching the coated side.
Another test is the fingernail test. If you have sensitive nails, you can feel the difference in surfaces by gently dragging your nails at an almost right angle to the glass. The rougher side is the coated one.
There are other tests but these two work for me.