How do people in art galleries securely hang a large painting on the wall??

Question

I bought an Andy Warhol portrait which I want to display in my livingroom. The stretcher(frame) cant be modified in any way and there is no string or anything to hang since it is such a large painting. How can I securely fix the painting to the wall in the safest way possible? It cant be visible, like having it suspended from the ceiling on a wire, I want all the support to be behind the painting, not visible. What exactly would be the best way to hang it? I was thinking about using a wooden baton, but I am not sure if it will be able to grip the stretcher well enough to hold it on the wall, and I am unsure about how to go about it. The wall is concrete btw, so can you give step by step instuctions on how to do this?

Answer 1

When I worked in the National Gallery, London, the large paintings had a flat metal piece on each corner (hole in the middle for a s***w/nail).  I've certainly seen these in Hardware shops in the UK.  The men who hung the pictures made sure the wall was solid behind the pictures (this is another thing you need to check out if you have a heavy/large picture to hang).  Any decent art supplies store wherever you are will advise you, and may even have the fixings.