Nut husk in powder form.
Add a teaspoon of Bister powder to a spray bottle with 100ml water (3.38oz). Put the lid on the bottle and shake well until the powder is dissolved. Best is to use distilled water, if you need to preserve the mixture for a while.
For a lighter result add more water.
To intensify the color, one can also add a few granules of bister onto the painting and spread out with a brush.
The contrast is more obvious when you use Bisters on a lighter colored Powertex such as Ivory rather than on Powertex Bronze or Black.
Bister is not waterproof and always needs to be finished with Easy Varnish for outdoor artwork.