Mix with IPA (Isopropyl Alcohol) to make eraseable and/or heat-settable ink. Once dry (almost immediately) the black ink is blendable and eraseable. When you are happy with the results, cover with baking parchment and heat with an iron to fix permanently. Alternatively, bake in a warm oven.
Use dry as a powder - blend across a surface. Eraseable until heat-set as before.
Works as a resist to acid etching - removeable until heat-set so changes can easily be made.