flow Linear development with capillary-controlled flow can be per-formed in a variety of vessels that differ significantly in design and sophistication [2,19,20,25–27]. These are often categorized under the headings of normal (N-chamber) and sandwich (S-chamber),and in use, further subdivided based on whether the internal atmosphere is saturated (NS or SS) or unsaturated (NU or SU). Normal chambers have a depth of gas phase in front of the layer greater than about 3 mm. For sandwich layers the gas phase is