90 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in turn influence the melting of the glass, the removal of seeds and bubbles and the forming of the glass. In this work, which is being carried on at Massachusetts Institute of Technology and more recently also at Pennsylvania State University, we see a study which began as purely fundamental research, but which now has definite practical application. This new information should aid in the more efficient production of better glass containers. Along other lines, such as glass color, research has not been as productive and practical considerations have limited the advances. New colors are always being sought in glasses, but the glass technologist must use inor- ganic oxides and metals as colorants. The high temperatures of the glass melting process rule out the wide variety of vivid colors produced by organic dyes. Also, many of the colorants are rather expensive, such as the gold used in producing certain ruby glasses, or presently unobtainable, such as the uranium used in producing a striking yellow green. Other colorants are so weak that they must be used in very large quantities and the result is a change in the working properties of the glass that makes it impossible to form the glass by machine. However, with the advent of the plastic coated bottle, brilliant colors of practically any hue may be incorporated in the plastic covering that is placed over the glass bottle. This system was developed by the Wheaton Plastics Co., and Hazel-Atlas is now a licensee for the process. In this plastic coating operation the bottles are heated and dipped by machine into a bath of hot polyvinyl chloride plasti- sol. The bottles are then removed and cured to develop a smooth coating that is approximately one millimeter thick. This coating, besides providing any color desired, is pleasing to touch and provides protection of the glass against abrasion. The plastic coating also absorbs energy when struck and lessens the effect of impact blows. When the coating is used on aerosol containers, the coating provides a restraining skin that prevents flying fragments should breakage occur. A final possibility with the plastic coating is the incorporation of an ultra- violet absorbing compound in the coating to screen out the sun's actinic or chemically active rays. The short wavelengths of the visible spectrum and the near ultraviolet are the spectral regions in which most of the chemically active radiation falls. This covers roughly a range of 250 millimicrons to 450 millimicrons. The changes that take place under actinic action are losses of potency of drugs, changes in color, odor and flavor. Any of these can cause considera- ble damage to a carefully prepared product. Amber glass will effectively screen out these actinic rays, but amber suffers from a lack of esthetic appeal. Accordingly, there has been considerable interest in ultraviolet absorbing materials that would either be colorless or colored in a pleasing fashion.

NEW DEVELOPMENTS IN GLASS CONTAINERS 91 As was mentioned above, ultraviolet absorbers can be incorporated in the polyvinyl chloride plastisol coatings applied in the Wheaton process. The absorbing materials most commonly used are beta methyl umbelliferone and some of the hydroxy methoxy benzophenones. These materials can also be incorporated in thin films of harder transparent polymers. Ceramic color coatings can be applied by spraying and fired into the surface of the glass. These coatings stop ultraviolet radiation as well as provide a decorative film. They are cheaper to apply than dipped plastic coatings and yet provide an extremely wide range of colors. Cellophanes and lacquers will also provide a considerable degree of protection if they are the right color. Irradiation by high energy electrons or neutrons is a possible method of changing the color of glass. Small quantities of certain rare earth oxides can be incorporated in glasses which will cause the glass to develop unique colors after irradiation. If the bombardment or irra- diation is properly masked on the glass surface, it would be possible to outline printing or trademarks and have the label for the product actually in the glass. While many plastics degrade after exposure to high energy radiation glass suffers no ill effects in its physical properties. Recent engineering progress has led to many refinements in the forming of glass containers. Much of this progress has been in the field of heat transfer and temperature control. These advances have enabled con- tainers to be manufactured with considerable reduction in weight. Ex- tremely light weight containers, however, have been made only in a few •cases where a large volume of production could be maintained without iinterruption. Glass container design becomes particularly important when light weight Icontainers are manufactured. With reduction in weight, it becomes [particularly difficult to maintain uniform wall thickness in the containers. lit is extremely important in these circumstances to avoid abrupt changes iin the direction in the container surface. Sharp corners should always be lavoided. The thin walls of light weight containers are quite susceptible to break- [age if they are abraded. Bottle coatings to prevent abrasions are really icalled for with most light weight containers. Where glass containers for aerosols are involved, one does not want a [light weight bottle. Glass aerosol packages should be reasonably thick [(around 1/8 inch thick) to give them strength and well designed to avoid Ibreakage. If rounded corners are used (a/16 inch minimum radius), Ilarge panels avoided and the shoulder sloped gently up to the neck no [problems should be encountered. It is to be remembered that a circular Icross section is stronger than an oval cross section and both are sub- Istantia]ly stronger than a rectangular cross section where internal pres- tsures are involved.