It also counts as old school because it was used as a method of duplicating things in Australian schools in the very late 1800s and early 1900s. As someone interested in printing techniques, maps, and DIY, this really took my interest and became a household project. So, I thought I'd share.
(When there's an excuse to draw maps and experiment with new stuff, we rarely need to be asked twice around here)
The method is called Hectograph printing. It's not hard to do, but requires a few specialist tools and ingredients.
First you need to make a gel bed, then you need a sheet of old style carbon paper (this was actually the most difficult thing to source), some tracing paper, the thing to be printed, and a sharp pencil or stylus.
Let's start with the gel bed.
This needs three ingredients and a glass or ceramic tray (don't use metal trays as the gel mix gets contaminated very easily by rust/corrosion).
For this bed, we mixed 60g of gelatine, 375ml of glycerine, and 250ml water, in a bowl over slow heat on the stove until the whole mix had dissolved into slightly cloudy liquid.
The mix was then poured into a glass tray, any bubbles on the surface the carefully popped with a pin or pushed to the side of the tray where they wouldn't disrupt the smooth printing surface.
This was left overnight, thus giving us the gel bed for the printing process.
The gel bed accepts a layer of ink from carbon paper, and it is this ink that will be used for printing. Apparently it will run about 30-40 prints with good carbon paper (about enough for a large school class) before the ink gets used up and the images start getting too faint to use.