Aceto-orcein (2%)

Orcein powder, synthetic (Gurr; e.g., CTL Scientific Supply)

Acetic acid (45%)

Prepare 5% aceto-orcein by boiling synthetic orcein powder in 45% acetic acid for 45 min in a reflux condenser. Use 45% acetic acid to dilute the solution to 2% orcein. Before use, remove particulate matter from aceto-orcein, either by filtration through blotting paper or by centrifugation in a microcentrifuge.