Successful design of architectural concrete is likely to require the knowledge of the structural engineer. The imaginative building concepts of the architect must be checked against the capabilities of the materials and against constructional feasibility. One of the main resources of the structural engineer is his/her knowledge of formwork, since this is such a large part of the cost of concrete and particularly of architectural concrete. The engineer can advise about the cost of forms and whether the proposed forming techniques are practicable. The engineer can also advise the architect about practical matters of obtaining texture- the effectiveness of various forms and formliners; the suitability of sandblasting, bushhammering or acid etching to remove mortar from the surface of the concrete chosen; the durability of aggregates; potential dangers of staining caused by impurities; or potential problems from variability in hardness of aggregate. The engineer must also give advice on how to achieve uniformity of appearance with the materials and methods selected. Finally he can help with color. Color adds one more degree of freedom to the architect, provided he can actually achieve what he desires. Producing consistent color requires attention to many details, whether portland cement is used alone or with pigments added. Variations in materials proportions, form release agents, vibration, curing time and temperature or finishing procedures can all affect uniformity. The engineer can advise whether the architect can achieve what he wants and, if it is possible, set up the specifications for doing it.