This monoprint (a demonstration piece for a local art group a year or so ago) turned up while doing yet another half-hearted studio clear up. I thought it might be interesting to do a second print on top and then work back into it.
The initial print was done with gouache, mixed with water to the right custardy consistency, and a few drops of gum Arabic added. I have a large sealable acrylic palette with many separate wells which I have over time filled with various mixes and colours; when a mix gets too dirty I replace it with something new and fresh
To get the registration right I put the piece of acrylic on the print and drew the image with a Posca pen, then turned it over and painted the extra details I wanted on the other side. Reminder, images are transferred in reverse onto the paper, so in this case had to be painted in reverse in order to print the right way round onto the existing image. I do hope that makes sense.
Not much detail added, above
Spraying the original print, above, so that the paint on the acrylic sheet will transfer. This is a somewhat unpredictable method, dampening paper in a bath and blotting it is better, but in this case it wasn’t an option.
In order to align the painted acrylic with the existing image I turn it over and laid it on the paper, above
Then turned paper and acrylic over carefully and rubbed the paper with the heel of my hand
The result is pretty subtle, above, perhaps too subtle; but with a little bit of brush work, below, I am done and resisting the temptation to get too fiddly.
kateosborne 
Amazing!