Once Abundance has sent the digital files to Links Signs, their artworker confirms that the transition from 6inch square original map to 3m square mural hasn’t disintegrated into pixels. This then comes back to Abundance to sign off, and at this stage, there is occasionally a technical digital issue that needs resolving – the date has fallen off the caption! why do the lines look all fuzzy? Then there ensues a technical discussion about bitmaps, vectors and greyscales and the artwork is twiddled and re-issued.

Each map is made up of three panels. Nearly all the panels have now been sprayed pale blue, and we have chosen pale blue clips and pale blue frames to hold everything in place. There are 16 maps and one credit panel. Each map has at least two colours (black and river blue) but many of them have more.

A detailed acetate film is printed off for each colour; this takes about 4 hours per colour.

Then goo (aka photo sensitive emulsion) is smeared onto the acetates. Ultraviolet light is used to harden the goo, and then the surplus is washed off leaving the negative which is used for screening.

The warehouse is stacked full of these green mesh screens. In the picture below the front five screens are all labelled panel 6, which is the right-hand (third) panel of the 1700 map.

The artworker has a little sketch stuck on his first aid box as an aide memoire and the pale blue metal panel is clamped onto a workbench. The relevant green screen is loaded up; in this picture you can just see that the pale blue line that runs below the river has already been laid. The screenprinter loads up his machine with yellow ink and then screen prints the yellow across the panel, which is a very physical process. The yellow patch looks unformed, but once the black lines are laid over the colours, the map begins to take shape.

The panel will then be baked. Two colours that touch each other cannot be baked at the same time; some colours require higher temperatures at a completely different setting. All of the panels will have multiple bakings. Once done, this panel should match these two, with Sarah and me standing by it for scale, Sarah flashing her broken cycle arm. The white square is where the artwork, in this case an engraving by Knyff of Chiswick House, will be added at a later stage, using transfers rather than screen printing. That’ll be another blog …