Holbein Duo-Aqua Oil is an artist quality watermixable oil paint made with water-soluble linseed oil. To make DUO identical in every respect to its traditional professional grade cousin, Holbein developed a unique additive which works as a surfactant, any residue of which loses its effectiveness once the oil color is dry. 
TIPS FOR WORKING WITH DUO
  
Drying time is comparable to traditional oil straight out of the tube (no water/mediums).
  
Water Will matte down the surface when mixed with DUO, like turpentine does to oil.
  
Quick Dry Medium or Painting Oil is ideal for glazing.
  
Traditional oil mediums may be used, but mixture will lose water solubility.
  
Traditional oil painting techniques apply for DUO (fat over lean).
 
Titanium White **** The most popular white, Titanium White is inert and non-reactive under most ordinary conditions. It has greater opacity than lead or zinc but tends to yellow in the short term. It is slower drying than lead but faster than zinc. It handles and mixes well, and its surface qualities may be strengthened by mixture with zinc oxide which also helps reduce the sometimes too intense tinting power inherent in titanium pigment.
 
Permanent White **** A titanium white with the same general handling qualities but with a barium sulphate additive which inhibits yellowing in early drying while reducing tinting power and increases transparency.
 
Ceramic White **** A painting white developed by a joint research project of the Holbein Works Ltd. Laboratory and Japanese Government Industrial Laboratory, Ceramic White was developed to combine the most positive qualities of other painting whites when taken collectively. It contains titanium and strontium pigment which will not react with sulphur. Ceramic White offers superior surface strength without brittleness, increases tinting and covering power over lead and zinc, but when compared to titanium white, it offers increased transparency, drying time and visual whiteness. Excellent handling qualities.