Page 16 - Demo
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Trying to de ne obscenity in Jacobellis v. Ohio, Supreme Court Justice Potter Stewart wrote “I know it when I see it.” Soapmakers often take the same approach in de ning “trace.” It is variously described as the stage at which it becomes possible to draw a pattern on the surface of raw soap. If this stage is reached too quickly, there is little time to craft colorful swirls and other patterns. If it comes too slowly, we are left impatiently wondering whether it will happen at all. What factors determine how quickly trace is
T race Evidence
By: Kevin Dunn
achieved? Is it possible to slow or hasten trace? To answer these questions, it will be necessary to de ne trace more objectively than would suf ce in a Supreme Court ruling.
What we are really describing in the trace phenomenon is that raw soap starts out thin and watery, becomes thicker and more viscous as time marches on, eventually becomes so thick that it cannot be poured, and  nally solidi es. The transition from liquid to solid is gradual, not sudden, and we may talk about a “thin” trace or a “thick” trace. To quantify this nebulous quality, we really need to talk about viscosity, a property that can be de ned and measured objectively.
Figure 1
The unit of viscosity is the Poise, but the more practical unit for soapmakers is the centipoise (cP). At room temperature for example, water has a viscosity of 1 cP. Olive oil, castor oil and glycerol have viscosities of 84 cP, 986 cP, and 1490 cP, respectively. The higher the viscosity, the slower a liquid moves when poured. There are several kinds of viscometers available, most of them too expensive or fragile for our purposes. One rugged option is the Norcross Shell cup, shown in Figure 1. It is essentially a stainless
Figure 2

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