Would suggest adding 0.5 grams of Crystal Violet to 100 ml water. Mix well to dissolve. Then add 20 ml methanol. IF this solution results in overstaining of the plaques, prepare a fresh solution with a lower percentage of Crystal Violet
A published procedure for plaque assay titration is not available. The methods listed in the literature vary widely from source to source. Some procedures will fix the plaques first with either methanol or acetone. Other procedures will dilute the Crsytal Violet at various percentages. The percentages can vary from 0.5% to 0.001% depending upon the source. The various sources typically state the crystal violet solution should either be prepared fresh or stored no longer than 1-2 weeks at 4°C.