A little analog help

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Hi all,
I keep wondering how it was that Andy Warhol mnge to have the dot grid raster in his black overprint plate.

How can I reach the same without using anz computerisation. How did he enlarge the pictures he used and what was the medium he used to expose the mesh? He certainy could not printthe photo on 40x40" transparent film or even bigger in case of his large canvases.

My goal is to reproduce the exact workflow he did. I am still missing the part between the moment where there is a photo of a person ( news or polaroid) and there is exposed mesh with dotted grid raster few hours later.

Anyone who still remebers how?

Thank you
Filip