Putty knife: 

Over all length 300mm with blade width of 38mm

Using a putty knife smooth the face putty on an angle ideally about 1mm to 2mm lower than the line of the back putty, this leaves a "painters line" so that when the putty is painted the paint can fully cover the putty and can go slightly onto the glass to ensure a good weather seal.

When the face putty and the back putty have been trimmed back to where they should be, then lightly brush off with the duster brush, this smooth's off any feather edges and ensures that the putty is fully sealed against the glass.

Wait for the putty to skin off before using a good quality primer and then finish painting with top coats.

Painting the putty and onto the glass up to the "painters line" ensures a good weather seal and also protects the putty from drying out too much and becoming loose.