4. Spread 200 l of substrate solution over the whole surface of sample.
5. Lid the Petri dishes and incubate at ambient temperature for 0.5 h.
6. Check area of black melanins.
7. The darkening of a representative number of 1 cm2 squares of a slice can be
calculated using a 1 cm2 template overlay. Each square that is completely black is counted
and recorded as a percentage of the total number of complete squares covered by the
template.