PAINT AND PIGMENTS 229 



4. FAT, GREASE, OIL, AND SOAP 



Mixtures of these materials reveal their general character with a 

 0.2A+0.33X or a 0.2A— 0.25X diffraction plate in a 16-mm objective. 

 At higher magnifications the 0.2 or 0.14A±0.25X plate usually gives 

 adequate contrast. The number of phases in the system and the ap- 

 proximate amounts are readily determined with the phase microscope, 

 also the presence of lifiuid crystals, or other aggregates. Polarized light 

 sometimes is helpful with phase contrast (see Section 1). 



Microcrystals of paraffin were considered in the first section of this 

 chapter. The structure within a wax is often important and may be 

 revealed with the phase microscope. Figure Yl.l, A-D, shows the 

 appearance of the paraffin part of a section of liver embedded in a 

 paraffin block with the different contrasts. For adequate support 

 when thin sections are to be cut, the crystals must be small enough to 

 fill all gaps around and within the tissue. These sections were cut with 

 a microtome, mounted, and observed before the paraffin was re- 

 moved. 



The structure of a grease is important as well as its composition. 

 This can be seen in a direct sample, a melted sample, or after working 

 the grease between two microscope slides. Liquid crystals in soft soaps 

 may be seen, and some shampoo soaps make good demonstrations. 



5. PAINT AND PIGMENTS 



Very dense fine colored pigments may be seen better with the bright- 

 field microscope, but the less opaque pigments show better with the 

 phase microscope. It is possible to evaluate grinding and disperison by 

 direct examination of the product, likewise emulsification when liquid 

 components are dispersed in the product. The shape of colorless, or 

 slightly colored, materials may be seen within the limits of the optical 

 microscope. This may be important when the particles can become 

 orientated later from spreading by the paint brush, or roller. 



Sections of painted or varnished wood or other material may be 

 examined and the surface protective layers measured with the phase 

 microscope. The nature of enamel surfaces and the effects of abrasion 

 and weathering have been studied with the aid of ethylcellulose replicas 

 by Richmond and Francisco (1949). The phase microscope reveals 

 more detail in replicas than the brightfield microscope, and low to 

 medium contrast phase objectives in either bright or dark contrast are 

 appropriate. When reflection from the surface is adequate, phase 

 vertical illumination should be considered. (See Section 8.) 



