MEASUREMENTS ON HUMAN HAIR 383 Sample Preparation The preparation of swatches consists of mounting the hair that has been selected to be used in the measurements, on the clamps previously described. The uniformity of this operation is facilitated by proceeding as follows: start by securing enough hair for a complete set of measurements. Six swatches are recommended in routine evaluations of products. If changes in comba- bility are very small, more swatches might be required to ascertain statistically significant changes. About 10 g of hair are requi•'ed to prepare each swatch. Although if could be desirable to use perfectly straight hair, this is not prac- tical because it is difficult and expensive to obtain such hair. Virgin European hair with its natural soft curl is perfectly suitable for these measurements and should be used. If possible, all the hair to be used in 1 set of measurements should come from the same batch of commercially purchased hair. Blending the hair is not necessary and is not recommended because the coherence of the hair's natural curl is lost, and this results in excessive tangling. The length of the individual hairs to be used should be uniform. A good length to start with in preparing swatches is 11 in. Measure the length of the hair in inches. On a top loading balance weigh (to 4- 0.2 g) individual bundles of hair (one for each swatch) so that each COMB -:• top view side view CLAMP top view side view o 1 I • • , INCHES Figure 4. Top and side views of comb and clamp used in measurements

384 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS bundle's weight in grams is approximately equal to its stretched length in inches times (0.7) that is, the linear density of each bundle shotfid be proximately 0.7 g/in. Handle the bundles gently so that the hair's natural curl is not unnecessarily disturbed. Placc the rootend section of a bundle in the throat of the clamp and dis- tribute the hair evenly throughout its width. Allow approximately i in of hair beyond the throat of the clamp. Secure the male part of the clamp to the other part by means of the 2 screws. Proceed in the same way with the rest of the bundles. Cut the excess (root end) hair close to the top of the clamp's jaws. Stretch the hair swatch with the hands and cut the tip end of the hair at a distance of 6.5 in. from the closest end of the clamp. This can be done conveniently using a laboratory guillotine.* The amount of hair freely hang- ing from the clamp will weigh 4.5 to 5.0 g. The hair mounted on the clamps should be cicaned in order to remove dirt, grease, or any foreign material that might be present on the hair when it is purchased. The cleaning is done using a 15 per cent aqueous solution by weight of sodium lauryl ether sulfate. The (unadjusted) pH of this solution is in the range of 7 to 8. The solution is liberally applied twice to each swatch as if it were a shampoo. After the second application, the swatches are thor- oughly rinsed under running deionized water (at room temperature) for 30 min. For our purposes, this cleaning treatment is more realistic and less ar- bitrary than the commonly used precleaning of hair with various organic sol- vents. After cleaning, the swatches are combed and hung to dry and equilibrate to the standard conditions of 70øF (21.1øC) and 65 per cent RH for 24 hours in a controlled environment room or chamber. Experimental Procedure The experimental procedure consists of measuring the PCLs and/or ACLs of the same hair swatches wet and/or dr,v before a treatment and after the treatment. Measurements on Untreated Hair-Wet Measurements as •ollows. Step 1: turn on the Instron, allow it to warm up, and calibrate, following its operation manual. Step 2: place each of the swatches to be measured in deionized water at room temperature (70øF) for at least 10 rain and for no more than 30 min prior to the measurements. This can be done by supporting the swatches by the clamps and allowing them to hang freely inside a large beaker (• 3000 ml) full of deionized water. Step 3: take the first swatch out of the water and comb it until no derangling is noticed on further combing. Start this operation using *Harvard Apparatus Co., Inc., Dover, MA.