When a saturated powder is cooled below the freezing temperature of the interstitial water. the water sometimes forms ice lenses, which are layers of ice from which all particles have been expelled. To clarify the relationship between the rate of ice lens growth and the temperature Lit the growth surface, ice lens formation in a water-saturated, fine powder consisting of uniform-sized, spherical. glass micro-particles was observed in situ, using a microscope and a directional freezing apparatus. When the powder was frozen rapidly, the ice lenses grew faster, at lower temperatures. and formed thinner layers. The ice lens grew at a rate that was linearly correlated with the degree of supercooling at the growth surface, and was significantly slower than that of ice in water. The results suggest that the particles near the growth surface inhibit ice lens growth. (C) 2002 Elsevier Science B.V. All rights reserved.