You could be correct, but things such as a gel/wax really do stand out. I have worked on 3 different x-rays, and this is true on all of them. However, it is possible that the person operationg the x-ray is not paying attention or sees it and let's it go. It also depends on how full/empty the container is.

It would be a scary though if a bag check was called and they did not find the item and simply let the bag go. But that can happen too.

But I can not fell you how many times I have had to check a bag and the person believes they know what I am checking for, such as their tweezers or hair straightener, and that was NOT what I was looking for. I would have to be there while your bag is being checked to tell you if this item was whY they were actually looking for, which of course I can not do.

But I can promise you that clothing does not block or obscure the x-ray image at all, otherwise every bag with that in it would have to be checked. Just as the actual luggage itself does not block the scan of what's inside.