  An extended theoretical study of interface potentials in adsorbed
colloid-polymer mixtures is performed. To describe the colloid-polymer mixture
near a hard wall, a simple Cahn-Nakanishi-Fisher free-energy functional is
used. The bulk phase behavior and the substrate-adsorbate interaction are
modelled by the free-volume theory for ideal polymers with polymer-to-colloid
size ratios q=0.6 and q=1. The interface potentials are constructed with help
from a Fisher-Jin crossing constraint. By manipulating the crossing density, a
complete interface potential can be obtained from natural, single-crossing,
profiles. The line tension in the partial wetting regime and the boundary
tension along prewetting are computed from the interface potentials. The line
tensions are of either sign, and descending with increasing contact angle. The
line tension takes a positive value of 10^-14 - 10^-12 N near a first-order
wetting transition, passes through zero and decreases to minus 10^-14 - 10^-12
N away from the first-order transition. The calculations of the boundary
tension along prewetting yield values increasing from zero at the prewetting
critical point up to the value of the line tension at first-order wetting.
