An apparatus and method for characterizing gas flow through features fabricated in a hollow part. A pressurized gas is applied to an interior of the part, and this gas pressure flows outward through features fabricated in the part. At the same time, a stabilizing pressurized gas is applied to an exterior part skin; and the stabilizing gas has a controlled temperature differential from the gas applied to the part interior. An infrared signature of escaping gas and the surrounding part skin is analyzed by a classification method. Analysis of this infrared signature classifies the relative flow rate, size and position of the feature fabricated in the part.