How can we measure the water to soap ratio in lather?

I'd like to find a direct, repeatable. and reliable way to measure the water and soap content in lather.

I tried to measure it by making a lather and weighing everything before and after. One thing that's not clear is how to account for water in the brush. A second problem is the brush weight can change due to moisture and accumulated soap.

Here's what I did using

soap bowl before wetting: 136.1g
soap bowl 24 hours later: 135.5g
=> soap used?: 0.6g
brush dry: 55.1g (measured a day later: 56.5g)
brush pre-soaked: 62.3g
=> water used in wetting the brush: 7.2g
mixing bowl: 235.9g

Now I added water to the puck and made a lather.
bowl + brush after lathering: 309.8g
less bowl: 73.9g
less dry brush: 18.8g
less soap used: 18.2g
less wet brush: 11.0g (water added while making lather)

Using 56.1g for the brush:
percent soap with wet brush: 0.6g / 18.8g = 3.2%
percent soap without brush-water: 0.6g / 11.6g = 5.2%

I have two ideas to make this more accurate:

• Use a cream as it will be far easier to weigh the amount used.
• Source your water from a bowl, noting the amount of water used. You'd want to shake/drip your wet brush back into the bowl, of course.

Great idea! Nice to put that coke scale to good use, eh?

I am not a chemical engineer, nor do I play one on TV. I have thought about this problem, and do not think you can easily get the information you want. The first major problem I see is that the humidity in your test chamber (shave den) will affect your results enough to throw all your measurements off considerably. Humistats are expensive, especially if they are accurate.

I will guess that the variation I see when making lather is about 2 cc of water making a large difference in the lather I make using soap and brush.

Many soaps have a large/varying percentage of the ingredients as water.

Also, the cake will probably absorb some of the water.

It was 0.2g lighter a couple hours later compared to before using it. I let it sit for 24 hours and it's 0.6g lighter. Just one complication.

I think an answer to this came up in a soaping thread, if not elsewhere. The piece can be cut from the inside of the bar where moisture doesn't penetrate as easily.

The whole thing doesn't need to be too accurate. If we can measure 10:1 vs. 5:1, that's good. Being able to distinguish 7:1 vs 8:1 would be much better. At some point, individual taste in lather would predominate. Nevermind different soaps--that variation is a given, and might need separate tests.

Finally, if we can find an easy way to replicate the test, everyone can check against each other.

You do not need to get so anal about the amount of water you use. After all, it's called the "Art of Shaving". There is some art and a feel to the state of the lather to find out what is best for you. You will have to shave some to find out what you need. It's always YMMV. I don't care if you are using soap or creams. Start with a fairly dry brush and then if the lather needs more moisture then add a few dribbles from the faucet. Each soap/cream/brush and face is different. You will have to adjust it for you.

dcrosso said:

You do not need to get so anal about the amount of water you use. After all, it's called the "Art of Shaving". There is some art and a feel to the state of the lather to find out what is best for you. You will have to shave some to find out what you need. It's always YMMV. I don't care if you are using soap or creams. Start with a fairly dry brush and then if the lather needs more moisture then add a few dribbles from the faucet. Each soap/cream/brush and face is different. You will have to adjust it for you.

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That's good advice, but not the point of this thread. I've kind of been bent on learning something about the science of shaving lately. Aside from taking picture of [thread=95526]razor blades[/thread], [thread=123578]hair[/thread], and [thread=184600]lather[/thread], I've checked the [thread=112991]pH of soaps and creams[/thread], created a Science of Shaving wiki page, and done a dozen failed experiments that I haven't posted about. Among other things, it would be useful to know the ratio of soap to water in preparing solutions for other tests.

Steve...I love that you come up with these useful and informative scientific posts. They are always fantastic to read.

I guess I did misunderstand. I thought you were trying to figure out a way to measure the optimum water to soap/cream ratio for the best shave. After rereading the post I still can't understand why you want to be so exact. With all the variables previously discussed and each shaver having a different face/beard it seems fruitless to me to quantify exact amounts of water for each shaving product. I guess that is what we do automatically when we gain experience shaving with numerous products, mostly through trial and error. Hopefully with not to many errors.

Make a bunch of lather without any weighing. Weigh the lather alone with a .001g precision scale. Let it dry. Weigh it again?

If I want to prepare a solution to soak hair and evaluate it for the effects lather has on hair, I need to know whether lather is 2% or 10% soap. If you add up the errors here, I really can't tell better than that. A 5 to 1 error is too much.

aimsport said:

Make a bunch of lather without any weighing. Weigh the lather alone with a .001g precision scale. Let it dry. Weigh it again?

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Excellent! It'll take a HUGE bowl of lather, but it'll work. Measuring and comparing the moisture content between the lather and soap will give the answer. Thanks.

This is actually quite easy.

Preweight a small plate, tray or piece of filter paper (a coffee filter will work fine).

Make up you lather using your typical process

Place a small amount of lather on the preweighted item, weight immediately.

This gives you the wet weight.

Allow to dry completely, you can accelerate this by placing the sample in a warm, dry place. Weight again, this is the dry weight

Do the math (dry weight)/(wet weight)*100 = wt% soap in lather.

Drying doesn't work for soaps containing sodium silicate or more that 1% glycerin or from highly unsaturated oils such as linseed oil. The alternative doesn't look too bad.

http://www.freefictionbooks.org/books/s/22783-soap-making-manual-by-e-g-thomssen?start=72

Assuming you are able to determine the exact soap/water ratio for a particular soap, under certain barometric pressure, humidity and altitude conditions, then what? The variables cannot be controlled, so the experiment is meaningless, isn't it? What is a lather? When does it become "good"?

Codfish said:

Assuming you are able to determine the exact soap/water ratio for a particular soap, under certain barometric pressure, humidity and altitude conditions, then what? The variables cannot be controlled, so the experiment is meaningless, isn't it? What is a lather? When does it become "good"?

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I can't think of any way this can help someone improve their lather. The goal is to roughly measure both how much soap is used in a shave and the soap concentration in a typical lather.

Like you said, there's not much point in being too precise, so I think we can dispense with barometric pressure and temperature, but humidity is significant if the brush and soap are to measured, only because the amount of soap is so small that it can't tolerate large errors. The method suggested eliminates the water, so this problem (hopefully) goes away.

The simplest thing to do is weigh a soap, shave, then let the soap sit for a few days, and weigh it again. That gives how much soap is used. Taking this measurement many times should give a good answer for how much soap is used. It doesn't provide any answers for soap concentration, though.

SiBurning said:

Drying doesn't work for soaps containing sodium silicate or more that 1% glycerin or from highly unsaturated oils such as linseed oil. The alternative doesn't look too bad.

http://www.freefictionbooks.org/books/s/22783-soap-making-manual-by-e-g-thomssen?start=72

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I don't know why you believe this to be the case. Are you concerned that these constituents will evaporate? Glycerin has a boiling point of over 500 deg F, so I don't see how there is going to be a significant loss. Sodium Silicate hardens quite nicely as it dries, it is in fact used as a binding agent in a number of industrial applications. Most oils (fats) in the mix were converted to soap during saponification, any super fat will stay behind as an oil.

Are you actually trying to determine the percentage of soap in the lather or the percentage of soap plus other ingredients in the puck, because your soap puck almost certainly contains water.

My last tube of Omega cream (147g) lasted me 147 days. I used 1g/day, didn't I? I shave once a day, so that equals 1g per shave.

Or am I missing something? I think you are over-complicating this. It's not that difficult. I would argue that use over time is the variable to measure. The water/soap ratio of lather would seem to be subject to many variables including humidity, in my opinion. My "lather" could have ranged from 100% product to 100% water, but was most likely somewhere in between. But IMO, the proper shave mix is dependent on a mixture of variables that makes accuracy impossible and generalization somewhat meaningless.

fccexpert said:

I don't know why you believe this to be the case.

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I looked it up. This is standard practice for measuring moisture in soap.

Codfish said:

My last tube of Omega cream (147g) lasted me 147 days. I used 1g/day, didn't I? I shave once a day, so that equals 1g per shave.

Or am I missing something? I think you are over-complicating this. It's not that difficult. I would argue that use over time is the variable to measure. The water/soap ratio of lather would seem to be subject to many variables including humidity, in my opinion. My "lather" could have ranged from 100% product to 100% water, but was most likely somewhere in between. But IMO, the proper shave mix is dependent on a mixture of variables that makes accuracy impossible and generalization somewhat meaningless.

Click to expand...

I think you're looking at this from the point of view of shaving. I'm thinking in terms of testing & quantifying things. From my point of view, that last part would be a cop out. If the variation is wide enough to be a range, and if there's some variation, that's all good to know, but I'd like to know what the numbers are.