After a couple of sessions on this painting I've come to the realisation that some skills are retained while others are lost - hopefully only temporarily - if they're not exercised regularly. As the saying goes, "use it or lose it".
The preliminary drawing went well enough and some areas of the painting were also trouble free, but my perception of tonal value and colour is in desperate need of refinement after a long break. Mixing the desired colour is challenging enough, but where I'm having the most difficulty is in arriving at the correct tonal value - I hope I haven't overplayed the darkest areas within the painting.
After a rummage through my old art materials I rediscovered this simple but invaluable tool designed for the tonally challenged. It's a terrific aid whether I'm drawing or painting and I use it constantly to check and compare tonal values within my work.
If your eyesight is as lousy as mine and you can't read the text on the image above, click it to open an enlarged view.