is about 10 minutes and hardening is attained after 20 minutes in a variant of this example to the beads treated as above and bearing the polymerisation catalyst are added glass beads bearing a coating comprising a first substance which if it were used alone would render the beads hydrophobic while leaving them oleophilic and a second substance which if it were used alone would render the beads hydrophobic and oleophobic these beads are treated in accordance with the method described in belgian patent 904 453 so as to obtain good distribution of these beads in the resin and confer reflective properties on the latter said mixture is used to mould reflectors solid glass beads with a median diameter of about 400 micrometers are treated with a mixture of interox bp 40 s trademark from peroxid chemie gmbh and silane a174 interox bp 40 s is a 40 suspension of dibenzoyl peroxide in phthalate this mixture adheres well to the beads and there is no need for any positive drying of the beads after treatment the phthalate plays the role of plasticiser in the resin in this way 0 3 g silane and 2 5 g catalyst per kilogram beads are fixed to the beads the treated beads are useful for incorporation in retro reflective acrylic paints chopped glass fibres are mixed with a solution of silane a 174 and benzoyl peroxide in.