% of water evaporates/label

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heidwil

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I am trying to figure out how much water will evaporate in CP soap that is cut almost 1 inch thick and will cure for 4 weeks and some also 6 weeks. What weight do I put on a label when I know that after 4 weeks the soap will continue to lose water and the weight written on the label will be wrong. I know 6 weeks would be better but they have to be done after 4 weeks. Does all the water evaporate or just a % of it? Do I need to write the weight on the label as I weigh it or some % less? What do you do?
I don't like to cure it just 4 weeks and will be more careful next time!
 

The Efficacious Gentleman

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Depending on your recipe it will stop losing water at some point. So as you still have your bars up to 12 weeks after cutting you can measure one regularly and monitor when the weight loss becomes next to nothing. That weight, or a little bit less, could be safely put on the label
 

DeeAnna

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Most of us who have shared what we do here on SMF usually understate the weight by a comfortable margin so we are reasonably certain the soap will weigh that much and usually a bit more by the time of sale. It's a bit of a guessing game, but weighing your soap over time will give you some basis for making a reasonable guess.

The point to putting a net weight on a label is to give the consumer at least that much soap, but there's no law that says the soap must not weigh more than the weight on the label. The consumer gets more value for her money, so who is going to complain? If a bar of my soap after a 4 week cure weighs 145 grams and another weighs 170 grams, it doesn't matter -- the weight on the label for both says 128 grams (4.5 ounces).

In my experience, soap will lose weight pretty fast in the first 4-6 weeks and then will continue to lose weight as more time passes, but at a slower and slower pace until it's so slow the weight loss is basically zero. It doesn't actually stop losing weight for at least the first year or so, however.
 
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KristaY

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I do just what DeeAnna outlined - weigh them then deduct a bit for the label. People will always complain if they get a bar that's under the stated weight but will never complain if it's more. :)

I've also tracked the weights of my various recipes so I know what to expect with weight loss % for each. It's certainly not exact as each batch will differ due to environmental issues, etc, but at least I have a loose guideline.
 

heidwil

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So the weight of the soap has to be at least as much as I put on the label.
If the soap was bought and after maybe 2 month the weight is a bit under, would that be okay then?
What percentage does a soap lose on water in about 4 month on average?

Thank you SO much for your help and replies!!
 

KristaY

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The percentage of weight loss is going to be specific to your recipes and where you live. It'll depend on the amount of water you use and the humidity in your area. Based on that, your weights at different times will probably be a lot different than mine. I use relatively low water and live in a very arid environment so my soaps lose a lot of water in the first 3 weeks then significantly slow over the next 3 weeks. From there it's miniscule over the following few months. I haven't tracked weight past 6 months because it pretty much stopped there for me.

So based on all that, I can't give you an anwer as to what to expect. You're going to have to track the weights of your recipes so you have a clearer picture of what your soaps are doing.

I apologize for being so vague but it's the best I've got!
 

DeeAnna

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The weight on the label is the weight at the time of sale, not the weight months after the item was purchased.

Think about buying vegetables, bread, or meat at the grocery -- these products lose weight over time too, but you would never take a loaf of bread back to the store and complain because it lost weight after you bought it. What you get at the time of purchase is what you pay for.

I agree with the others -- you need to figure out the rate of weight loss for yourself. It depends on season of the year, the kind of soap recipe, the packaging, the shape and size of the bars, etc. It's pretty clear you intend to sell or have already sold your soap, so look at this testing as some of the ongoing training required to successfully run this kind of business.

...If the soap was bought and after maybe 2 month the weight is a bit under, would that be okay then? What percentage does a soap lose on water in about 4 month on average?...
 
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The Efficacious Gentleman

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As above - you have to weigh yours until you know when it stops losing weight. But to be honest, unless you're selling you really don't need to label at all!
 

heidwil

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I truly appreciate all your help and will start putting a little less weight on the label. Thank you!!!
 
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