Cabosil M5 untreated silica is a fine white synthetic amorphous colloidal silicon dioxide (similar to Gasil 23). It has an extremely small particle size of 0.2 to 0.3 microns. It is a versatile filler which has won favor with many art conservators in Europe; we are pleased to be able to offer it in the US. Cabosil M-5 is particularly versatile. Try it with lacquers and pigments, where its small particle size offers advantages over other fillers.