Reccomended%20by%20Hydro%20offices%20for%20chart%20correction.Finest%20airbrush%20colours%20from%20Schmincke%2C%20extremely%20lightfast%20and%20brilliant.%20These%20were%20especially%20developed%20for%20the%20spray%20gun%20but%20can%20be%20used%20equally%20well%20with%20ink%20pens%2C%20technical%20drawing%20pens%20and%20brushes.