After some trial and error, I arrived at a healthily glowing design.
The mushrooms are constructed with transparent silicone (acetoxy cure), tinted with a drop of liquid watercolour.
I moulded the main body sections by sandwiching the silicone between layers of cling film. The rounded caps are formed by stretching this over a large marble. The stalks by rolling into an even stick with the wires embedded in the silicone.
The gills sealing the underside are silicone spread over a section of cling film gathered in the centre and stretched.
Each cap contains an SMD LED and some scrunched-up cling film that acts as a diffuser.