Method for mixing colorant with a viscous material

A mixing method employing a tube of viscous material wherein the tube has a sealed dispenser end section, a filler end section having surface portions defining a fill opening into the tube, and a thrust cap slidably mounted in said filler end section, said method further employing a mixing apparatus having a mixer seal structure adapted to seal and frictionally lock against surface portions of said filler end section during the mixing operation, wherein a mixer shaft is slidably sealingly mounted thru an axial bore in said seal, and wherein a mixer impeller is fixed to a distal end portion of said shaft for movement therewith said tube, said method comprising performing the steps of (a) removing said thrust cap from said tube, (b) adding colorant into contact with said material within said tube, (c) placing said mixer seal sealingly against said surface portions of said open filler end section to seal said fill opening with said impeller inside of said tube, (d) starting reciprocation of said shaft within said tube (e) continuing the reciprocation for a desired mixing period, (f) removing said seal, shaft and impeller from said tube and from the now colored material therein, and (g) replacing said thrust cap in said filler end section to retain the colored material in said tube.