STABILITY TESTING OF :. for use 'in any stability programme. Two or more or production batches, prefer- made from different lots of materials, should be used for the •final tests if they are to have any value. With these facts in mind, and with understanding of the limitations accelerated stability tests, I can •i%•i'• on-to discuss such tests for specific :{)!!.•i?ihair preparations. 'Raw material 2':•i•i': Control will not be included, although •'• •/•:?i'its importance' should not be mini- ½•!:i!:mised. The stability or instability ? ?of a cosmetic product very often !'?:i'depends upon the quality and control :)71( iof the raw materials used. :i i •!: 5 •' I shall limit my remarks to three ) !::)!ilVery popular t?pes of hair prepara-. ! ?):?}!'tions, namely cold wave solutions, :J?: shampoos, and hair-setting cosmetics. (iT!:/:'.:Dr. William Colburn has .already •.'•::':::::' ably discussed the stability testing :,:i!!i!.1øf emulsions (this Journal, Vol. 2, 3), and so I shall not attempt .. to discuss emulsified hair creams and lotions. TESTING COLD WAVE :. PREPARATIONS !i:•'•:" Most cold wave preparations 'on the market to-day consist essentially of an aqueous solution of thiogly- collic acid (usually as the ammonium !•i:.: salt) and an excess of alkali to bring :!',( the' pH to about 9'0-9'6. They' : may also contain a wetting agent to facilitate penetration into the hair, a clouding or opacifying agent to ": : impart a milky white appearance to the product, perfume, and colouring matter. The solution is usually HAIR PREPARATIONS packaged in 3 or 4 ounce bottles that are either sealed with a paraf-' fined cork plus a metal cap or a' plastic cap that has a vinylite liner. There are a number of difficulties that can occur in a packaged cold wave solution: 1. The thioglycollate concentra- tion can drop. The active content of thioglycollate salt can be deter- mined by iodimetr/c titrationi This drop can be due to inferior raw matedhals or to a defective seal. Thioglycollic •cid is easily oxidised to dithioglycollic acid, especially in alkaline solution in the presence of traces of metals, such as coppro or manganese, which catalyse the oxida- tion. 2.'The pH can drop..The pH of cold wave solutions must always be kept within a rather narrow range in order that the solution shall function properly when applied to the hair. Reaction of the alkali with the wetting agent or with the emulsified oils may cause the pH to drop. 3. Discoloration of the liquid ma.y occur." A pink colour is caused by. iron, which may have been present in one of the raw materials, in dirt or dust in the bottle, or may have got into the solution by corrosion of the metal cap. Only one part of iron in four million is needed to' turn the solution pink, so the impor- tance of keeping cold wave solutions free from iron is obvious. A yellow discoloration may appear, especially where a poorly paraffined cork has been used to seal the bottle. The tannin becomes extracted from the cork, resulting in the off-colour. ß 183

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS' 4. Breakdown or separation of the emulsified oils. This can be a very serious problem in cold wave solu- tions that have a white or milky appearance. The clouding agent must be selected with great care and the finished product subjected to thorough testing in the laboratory. 5. Perfume difficulties. Perfumes have. noi: been too successful in covering the ammoniacal and thio- glycollate odour of cold 'wave solu- tions, but they are used in many preparations. Although the odour character of the perfume may change with age, a far more serious problem occurs when the perfume oil is thrown out as small globules. 6. Fading or change in colour when dyes or other coloring matters are used. ß Since cold wave solutions are powerful reducing agents, many dyes which may be used to colour the solution .are unstable. Very few of the certified colours show satisfactory stability in cold wave solutions, but accelerated laboratory stability tests ,will usually weed out the dyes that are unsatisfactory. ß 7. Formation of sediment or crys- tals in .the solution. These are usually insoluble organic sulphur compounds and may be found when an inferior grade of thioglycollic acid is used. Any method of accelerated stabil- ity testing of cold wave solutions must be-able to evaluate both chemical and physical changes in the product. Two significant chemical changes which may occur are a fall in the pH value and in the thioglycol- late concentration. And changes. 184" which may alter the appearance of the product are emulsion breakdown, perfume separation, or discoloration. Bottled samples from each batch of cold wave solution should be shelf- tested for at least a year and exam- ined frequently to check for emul- sion breakdown or discoloration. They should be assayed for thio- glycollate by iodimetric-titration- and the' pH accurately .determined.- Samples can also be tested for heat stability at 100 ø and 120 ø, and cold tested at 35 ø to 40 ø F. Both heat and cold tests can run up to 30 days and longer, after which the solution is again assayed for thioglycollate and the pH determined.. Accelerated shelf tests, such as sustained heat at 100 ø to 120 ø, will .usually reveal whether or not the emulsion, per- fume, wetting agent and colour are stable and compatible in the presence of alkaline thioglycollate. During the early years of cold. wave development an accelerated test that was occasionally used was to bubble a/r through a cold wave solution and assay the solution at frequent intervals.' When ammonia • was used as the alkali the pH con- tinued to drop, due to loss of ammonia, and the rate of oxidation.: decreased. When fixed alkalis were used, the rate of oxidation often. indicated the presence or absence trace metal. catalysts or the effect,? • if any, of the various additives such: :. is perfume, clouding agent, we.tting?i agent, etc., on the rate of oxidatiom:ii: I An accelerated test that I have used was similar to this but precise. In an apparatus similar