Winsor & Newton Gum Arabic
A calligrapher's best friend. If you don't have this, you need it. Trust me.
Gum Arabic is a mild natural adhesive that binds runny inks into beautiful calligraphy inks. Add it to all of your favourite inks to help them adhere to the slipperiest of papers, thicken up, or just stick really, really well.
Ps-- Mix this with Pearl Ex, and you have yourself a metallic dream.