  The wetting properties of solid substrates with customary (i.e., macroscopic)
random roughness are considered as a function of the microscopic contact angle
of the wetting liquid and its partial pressure in the surrounding gas phase.
Analytic expressions are derived which allow for any given lateral correlation
function and height distribution of the roughness to calculate the wetting
phase diagram, the adsorption isotherms, and to locate the percolation
transition in the adsorbed liquid film. Most features turn out to depend only
on a few key parameters of the roughness, which can be clearly identified. It
is shown that a first order transition in the adsorbed film thickness, which we
term 'Wenzel prewetting', occurs generically on typical roughness topographies,
but is absent on purely Gaussian roughness. It is thereby shown that even
subtle deviations from Gaussian roughness characteristics may be essential for
correctly predicting even qualitative aspects of wetting.
