THERMAL TREATMENTS WITH A CURLING IRON 17 Figure 2. (a-f) Thermally induced damage phenomena commonly observed in dry hair fibers exposed to 50, 100, 150, and 200 sequential ten-second-long thermal treatments with the curling iron. individual hair fibers with the heated metal surface of the curling iron is a severe condition. The severe radial cracking of the cuticula during gentle uncurling of the cooled hair fiber in the dry state especially indicates that the long contact time of the fiber with the hot curling iron leads to cuticular damage. Uncurling in the wet or moist state when the fiber is swollen may reduce cuticular cracking.

18 JOURN Al OF COSMETIC SCIENCE Figure 3. (a,b) Typical topography of dry fibers curled for ten minutes without tension (0-g load). The f/m contact zone of hair fibers curled for ten minutes under constant loads of 10 g (Figure 4a), 20 g (Figure 46), and 30 g (Figure 4c, d) produces rather similar topog­ raphies, irrespective of the increasing tension during treatment. The inside of many curls displayed matting and compacting, as well as spotwise mutilation of the surface cuticle Figure 4. Typical topography of dry fibers curled for ten minutes under constant load of (a) 10 g, (6) 20 g, and (c, d) 30 g.

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