Achievement of uniformity of weathering requires explicit statement of the quality required. Misunderstanding of the quality expected can affect the price of bids, lead to the selection of the wrong contractor, put an unnecessary burden of the successful bidder who must produce higher quality than he had anticipated, lead to poor rapport between him and the architect, and produce results that satisfy nobody. Specifications must convey the architect's expectations in a number of respects that go beyond the requirements of strength and color. He must set standards concerning such attributes as: kind of texture, freedom from bugholes, permeability, freedom from cracking, dimensional tolerances, and uniformity of color. Each item in the list requires some adequate means of evaluating it to the architect's satisfaction, even if only qualitatively, but it should be made clear ahead of time what this method of evaluation will be. For successful weathering, the architect must choose suitable ingredients for the concrete and consider the kinds of metals and other material that will be in contact with it on the exterior surface. Most of the ingredients contribute to the color. Even when a material comes from a single source it is possible that there will be differences between shipments. Whenever possible enough material should be stockpiled for the whole job. Cements, which have a strong influence on the color of concretes, vary in shade not only from brand to brand but from plant to plant. Aggregates contribute significantly to differences in color. Pigments must be carefully blended to insure uniformity. Because many aspects of the formwork affect the quality of the surface the architect will have to communicate his requirements clearly. For satisfactory results on weathering concrete, plywood form surfaces should not be used more than three times: also, they should be coated with a good grade of synthetic resin. Steel forms and fiberglass reinforced polyester resin forms normally provide uniformly non-absorptive surfaces.