Do the Numbers Matter?
There seems to be some debate in soap making as to whether or not the “numbers” matter. When I use the term “numbers,” I speak of the range of suggested values as you see in the image above: bar hardness, cleansing ability, conditioning quality, bubbly lather, creamy lather, iodine number, and INS number.
A hard bar of soap is generally preferred because it will last longer. All soap is cleansing, but some feel that soaps with a higher cleansing value can be more drying, while others may want a more cleansing soap for certain purposes. Soapers generally want their soaps to be conditioning, which makes them gentle. Bubbly and/or creamy lather is desired because it makes it easier to create lather. The iodine number can give soapers an indication of the bar hardness (lower number) and softness (higher number) as well as the bar’s conditioning quality (higher number). The INS number is believed to predict at a glance many of the other bar properties of hardness, cleansing, conditioning, and lather. The ideal INS number is supposedly 160.
But do these numbers really matter? There is some debate among soap makers as to their value. Two different perspectives from two respected soapers, for example, are Anne-Marie Faiola and Jasche Homemade Soap (dead link removed). Neither recommends that you either adhere completely to the INS calculation or deviate entirely from it in formulating your recipes. In fact, both posts I linked advocate a common-sense, test-it-yourself and see-what-works-for-you approach to using the INS numbers.
On the other hand, I have found looking at the numbers to be helpful in creating my own recipes. most of which have an INS in the range of 140-160. My own experience has been that soaping in the 140-155 has been my personal sweet spot in terms of all the qualities I want in soap. I think the INS number is an excellent guide for soapers creating their first recipes, but I also think it’s a good idea to experiment and research what oils actually do. Anne-Marie has just recently published a great guide to soaping oils. I plan to import the handy PDF she shared in that post into my Evernote soaping notebook.
Recently, when I was formulating a recipe for a dry/sensitive/mature skin facial soap, I did a great deal of research into the different properties of oils and other additives. Because I do not have dry skin or even very sensitive skin, I asked several testers to try it out and let me know what they thought about it. The feedback was generally quite positive. However, if I had gone by the numbers alone, I might have been discouraged from even attempting the soap:
As you can see, the hardness number is on the very bottom of the suggested range. And yet, the bar feels quite hard, possibly due to the unique quality of the olive oil I used, which though it has a low hardness value, actually produces quite a hard soap if given a longer cure. The cleansing value of 10 is off the chart, which may be desirable in a soap for dry or mature skin. The conditioning value of 67 is near the top of the range, which is also good for dry/mature/sensitive skin. The bubbly and creamy values are within the suggested range. However, the iodine is much higher than suggested, and the INS number is much lower than suggested. If I had formulated this recipe early on in my soap making adventures, I might have discarded it as having an INS that was too low, but I know this is a good soap now that I can read the numbers more critically. Rather than paying attention primarily to the INS number, I tend to look at the ranges for hardness, cleansing, conditioning, bubbliness, and creaminess and experiment with oils in my recipe until these numbers fall in the ranges I am looking for—which may not always be, as you can see, the suggested ranges.
So do the numbers matter? Frustratingly, the only answer I can provide is both yes and no. I think it depends on your level of experience in creating recipes and your goals for your resulting soap. I think soap makers who completely ignore the numbers possibly do so to their detriment, but I think soap makers who adhere to the numbers slavishly may also be missing opportunities to create wonderful soap that doesn’t fall within the suggested ranges.
If you are a soap maker, what are your thoughts about the numbers? Do you use them? How? Do you discard them completely? Why? I would love to hear your thoughts in the comments.
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