======================+=============+===========+====== | |Millimeters|Inches ----------------------+-------------+-----------+------ Barytes |3 coats (sum)| .1068 |.00421 |Single coat | .0356 |.00140 | | | Inside. White on wood |3 coats (sum)| .1624 |.00639 |Outside coat | .0230 |.00091 |Next coat | .0443 |.00175 Field in photographs |Next coat | .0620 |.00245 |Penetration | .0294 |.00116 White lead |Inside | .0215 |.00085 |Middle | .0405 |.00159 |Outside | .0184 |.00073 |3 coats (sum)| .0811 |.00319 Asbestine |3 coats (sum)| .1840 |.00725 | | | Blanc fixe |3 coats (sum)| .1068 |.0042 |Single coat | .0356 |.00014 | | | Outside. White on wood|Outside coat | .1329 |.00523 |Inside | .1845 |.00727 |Penetration | .0737 |.00290 ======================+=============+===========+====== =Polar Micro-Examinations and Photomicrographs.= By Polar Micro-Examination is meant the examination of pigments under polarized light. A polarizing apparatus, though not an essential in the hands of the paint chemist, is nevertheless much to be desired, for by its help deductions may be drawn as to the contents of a paint, which by other means might not be possible. The polarizing apparatus as marketed by most manufacturers of the microscope is attached in the following manner: The diaphragm immediately under the sub-stage container is swung out and opened to its widest limit, allowing the insertion of the polarizer. This polarizer carries one of the pair of Nicols prisms and is countersunk to allow of the introduction of gypsum or selenite plates. The analyzer fits over the eyepiece on the tube. The use of polarized light upon paint is valuable on account of its action upon crystalline substances. The re-enforcing pigments, such as Asbestine, China Clay, Gypsum, Silex, Barytes, etc., are crystalline and consequently act upon the polarized light. In most cases these pigments are used in ready-mixed paints in small amounts, varying between 5 and 25%. When a slide containing a small amount--for example, less than 3%--of these crystalline pigments is examined under the microscope by ordinary transmitted light, they will often escape observation, owing to the small amount in which they are present. However, in the case of polarized light, this could hardly happen. [Illustration: Microscopic View of Barytes under Polarized Light]