Please check my maths

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PerthMobility

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Would some kind people kindly check my maths to confirm or not that I am correctly calculating lye and water for CP.

Thanks,
Mac



I should have said that after allowing for 5% SF the actual NaOH figure is 142grms. ( I hope)
 
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PerthMobility

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What are my margins of error? Variables from the mean? I am in the general area with my Excel SS compared to SoapCalc. My maths came from a somewhat weightier chem tome.
 

The Efficacious Gentleman

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For a 5% SF, if your figures differ from soapcalc in a way that means a 10% SF difference then I would worry. If your planned SF and soapcalc has a 1% difference or less, I wouldn't worry. The sap values are all vagueish numbers, as each tub of oil can vary to some degree
 

SuzieOz

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Hi again Mac,

All of my recipes I have reformulated to use 1000g of oils, (just for convenience sake). So far, running all recipes through the trusty lye calculator, all of them use 142 or 143 grams of sodium hydroxide, no matter what oils/butters I use.

I do notice you have a lot of water there - I usually use 330g of water (or 1/3 of the total oil weight). I think most more experienced soapers on this site tend to use less, but I'm still learning about lye/water concentration/discounts. And I don't have your science background so you're probably spot on, but I'm just thinking from my own experience 379mls seems like a lot of water. Anyone else ... ?
Ok, I ran your oils through a lye calculator using 5% superfat and came up with 140g sodium hydroxide and 330g water.
 
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DeeAnna

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SusieOz - He's using the "38% water as % of oils" method, and his number for water is valid on that basis.

You are doing what some people call "water discount." All that mysterious phrase means is that you're just using less water than Mac is. I would too. :)

More: http://www.soapmakingforum.com/showthread.php?t=55249
 
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SuzieOz

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SusieOz - He's using the "38% water as % of oils" method, and his number for water is valid on that basis.

You are doing what some people call "water discount." All that mysterious phrase means is that you're just using less water than Mac is. I would too. :)

More: http://www.soapmakingforum.com/showthread.php?t=55249
Oh my goodness, do you mean I've been doing a water discount all this time and didn't know it? 8)

I tell you, I seriously learn something new here every day! :)
 

DeeAnna

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To use "water discount" effectively and to get the most consistent behavior from recipe to recipe, it's best to use "water:lye ratio" or lye concentration and totally ignore the "water as % of fats" setting.

Water:Lye ratio and lye concentration mean exactly the same thing, just stated differently. I use lye concentration, but others prefer water:lye ratio. No matter -- just pick one and get used to it.

The "water as % of fats" is not the same as the other two. As the fats in your recipes vary, then "water as % of fats" will make your lye solution more concentrated or less concentrated in ways that work against you. You'll end up with more water in recipes that really would work better with LESS water and less water in recipes that could use more. It's not all that important how much water there is in proportion to the fats -- it's the amount of water in proportion to the lye that is critical.

The default setting of "38% water as % of fats" is typically about 27-28% lye concentration for a balanced blend of fats, but the lye concentration at that "38% water" setting will vary once you get away from that "balanced blend of fats." It can range from about 26% for castile (100% olive) to about 31% for 100% coconut oil. This can make castiles very slow to trace and prone to separate in the mold and make CO soaps trace far too fast and overheat during saponification.

***

Mac -- I see you are calling out your water as milliliters. Unless you're using a graduated cylinder to measure, you will get more consistency in your results if you weigh your water same as your other ingredients. I grant that it's less critical to be accurate on the water compared with measuring the fats and lye, but it never hurts to be as accurate as possible for consistency's sake.
 
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SuzieOz

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Thanks for the info DeeAnna - you've explained that quite clearly, or maybe I'm finally starting to get a handle on it :) It makes sense.
 

PerthMobility

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That is a very informative post, DeeAnna (lovely name) and I thank you. mls and grms have become completely interchangeable is Australian lingo these days and "yes" I actually use digital scales to weigh everything, solids or liquids.

There are very few occasions in domestic use, when a "ml" does not equal a "grm", certainly not in CP soap making where the two measurements are completely interchangeable. Unless of course I am missing something.

Back to the water for a moment. I have made up a small Excel spreadsheet for ease of use. I have added the total of fats and then multiplied by .38 (38%) to ascertain the amount of water to be used. The NaOH is then calculated using the SAP for the individual oils and added to that amount of water. Is this correct, please?
 
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The Efficacious Gentleman

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If you mean just for the water, then of course the measurements can be interchanged. For all else, including water with any additives in, then you need to be using (and talking in) weight not volume.

Cultural differences can have a huge impact on how things are taken by others - for example what the Americans call a 'bum bag' [emoji33]
 

PerthMobility

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"Down under" it is more likely to be solids in grms and liquids, no matter water the constitution, in mls. So in this case lye, oil and EO will be referred to in mls and NaOH will be referred to in grms. Packaging and labeling standards also reflect this "common usage".
 

DeeAnna

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... lye, oil and EO will be referred to in mls and NaOH will be referred to in grms...
How you PACKAGE a product is one thing. How you MANUFACTURE a product is another matter entirely.

In the US, solid materials are usually labeled by weight and liquids are labeled by volume, and I believe it's the same in the EU. That means there is not much if any difference between Australia and most of the rest of the world on that point. In chemical manufacturing, however, one must have a reliable, repeatable way of measuring ingredients, and weight is the best way to achieve that when making soap.

You cannot assume milliliters are interchangeable with grams unless you're talking about water, and that's only considered to be true in everyday usage, not in an analytical chemistry lab.

Soaping oils and most essential oils (EOs) are less dense than water. That means 1 mL of an oil or an EO is not at all the same as 1 gram of either. If you weigh out 1000 g of soaping oils in to one pot, and you measure out 1000 mL of oils into another, you will end up with quite different amounts in the pots. That means any soap recipe in mixed units (weight and volume) is not the same recipe as one using only one system of units (weight OR volume).

Last but not least, the saponification value is a weight-based value. You have to use weight units for the oils and lye to make soap correctly if you want to use sap values as your basis.

***

Here is how I would modify your spreadsheet to use lye concentration instead of "water as % of oils" to calculate the amount of water for a soap recipe.

Image1.jpg
 
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PerthMobility

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Thank you so much for this DeeAnna. What you write makes so much sense when I stopped to really think about it. I have happily incorporated your amendments into Excel. I now understand the reason for the discussion on the amount of water. It can be download HERE.

This is important to me/us as we are intending to start a small "club" of soap makers using as far as possible Aussie oils and aromas so we can cater to an ever increasing tourist market. Tourism is "booming" due a to a low AUD/USD (<.75c) and many people want to try locally produced soaps while they are here. We will be incorporating into our existing business.

Thanks again and please feel free to cast any other pearls of wisdom you have in our direction.
 

DeeAnna

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Your latest spreadsheet looks good, Mac!
 

PerthMobility

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Praise indeed, thank you DeeAnna. I have cleaned it up a bit more and have included a place for Sodium Lactate which may prove useful for some people.

I still need percentages for quite a few essential oils if anyone can me help me out, please. Latest version HERE
 
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