= Solution
The lamellae are \b[<ferrite> and <cementite>], together forming <pearlite>. The displayed quantity is surface height in an <atomic force microscopy> image. <Nital> preferentially attacks the <ferrite>, leaving it lower and therefore darker; the narrow raised <cementite> lamellae appear bright. This is not the same contrast mechanism as brightness in an optical micrograph. Faster cooling that still permits <pearlite> formation causes transformation at greater undercooling and generally gives \b[finer lamellar spacing]. Cooling sufficiently rapidly to bypass diffusional transformation instead produces other products, potentially <martensite>; it does not merely keep making <pearlite> indefinitely finer.
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