I referred to the knowledgeable Trish for advice on what to use to seal some parts of the painting. She recommended Acrylic medium. You can get gloss or matt and it is a simple case of brushing it on. Obviously it dries very quickly. This I have yet to try.
Overall I am becoming proficient with the techniques I need to hone in order to get a really good finish. Patience is in short supply as yet and even with trying to spread the load round a number of paintings it is a waiting game.
I have changed from painting on MDF to Ply which is lighter and has a lovely grain. As unpainted wood has now become a feature of the paintings this is an important consideration.
Currently I am finishing the edges of earlier paintings. I am splitting the edge between equal measures of painted surface and varnish. I am using yacht varnish - the same material as being used in the voids on the large triangular paintings. This takes a good while to dry but gives a lovely rich sheen.
I also need to look into different materials to use to sand down to a smooth finish. Especially for the varnish. I will ask John when I next see him.