These beautiful interference colours work best as glazes.
Imagine the colour that shoots out of a fire opal, except each colour is isolated. eg. Interference Violet goes on like an almost colourless glaze but violet fire picks up and reflects the light.
When mixing these interference colours take care not to mix too much with other normal colours or the opalescent sheen will be lost. Using them as a glaze is the recommendation.
40ml tube size