Marginal materials, examples

Marginalia enrich the pieces, making further connections to other fields, as well as explaining tangential concepts. Examples are given in Table IV. These sections are also meant to expose students to aspects of the history of chemistry and the biographies of chemists. Marginal materials also provide a multiplicity of entry points into the chemistry. Not every student will be excited by every area, but more students may see themselves connected to the field in this way. 

Some treatments are practiced so widely that untreated material is essentially unknown ia the jewelry trade. The heating of pale Fe-containing chalcedony to produce red-brown carnelian is one of these. Another example iavolves turquoise where the treated material is far superior ia color stabiUty. Such treatments have traditionally not been disclosed. Almost all blue sapphire on the market has been heat treated, but it is not possible to distinguish whether it was near-colorless comndum containing Fe and Ti before treatment, or whether it had already been blue and was only treated ia an attempt at marginal improvement. The irradiation of colorless topa2 to produce a blue color more iatense than any occurring naturally is, however, self-evident, and treatments used on diamond are always disclosed. 

These models, however, can be useful if estimates are to be made of operating costs. By assigning fixed and variable costs to each activity, average and marginal unit costs at each stage of the process can be easily calculated, which will assist in decisions regarding pricing policies or whether to buy in components and materials or make them on site. ATPLAN is an example of a network-based model of this type. 

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