18 is delivering about 250 pounds of colored topcoat compound per hour to block member 22 for example for every 250 pounds of colored compound delivered to block member 22 about 48 8 pounds of charcoal gray colorant must be added at feeders 64 66 timer 58 is appropriately programmed to send an actuating 34 on 34 electronic signal to feeders 64 66 every twenty seconds the 34 on 34 signal lasts for four seconds so that colorant is discharged from feeder 64 66 into zone 40 for four seconds with a subsequent sixteen second 34 off 34 period before the next coloring cycle begins as noted above the vent port 44 is normally used to remove undesirable volatile compounds from the processed material by applying negative pressure at both screws via the conduits of vent port 44 it is understood in the industry that without such a removal process undesirable effects such as blistering occur in the final product due to the novel use of vent port 44 in the present invention it is clear that no such removal of volatiles occurs in the inventive process yet no negative side effects such as blistering have been observed despite the absence of.