PURPOSE: To prevent stains of a detection material, and to enable repeated uses, by coating the surface of the detection material with a silicone resin for the method of development ability detection of a 2-component dry type developer.

CONSTITUTION: A 50mm long×20mm wide×2mm thick stainless steel plate is coated with a silicone varnish contg. titanium oxide dispersed in 40wt% of the solid of the resin to obtain a white detection material 1. As said silicone resin, a normal temp. hardenable or thermohardenable type resin may be used, and not only a pure silicone resin but also ones modified with acrylic, epoxy, alkyd, and the like resin can be used. Since no stain remain on the detection surface of the detection material made of silicone resin, similar sensitivity can be obtained even if it is used repeatedly.