Formula calculations grams or tap / bulk density

Im new and working on my first formula, a basic lotion that contains a liquid and one powder at 10%.

This is what i was thinking

Batch Size 1000 grams
Liquid = 900 grams
Powder = 100 grams

But I have been told that to get the weight in grams needed for the powder I should use the bulk density of the powder and x that by the % ie Bulk Density of 0.6 x 100 = 60 grams.

Please can someone clear this up for me ?


Comments

  • MakingSkincareMakingSkincare Member, Professional formulator
    What is the INCI name of this powder you are adding at 10%?  Why have you decided on 10%?

    Are you including a reliable emulsifier blend, stabiliser etc ? 
    Jane Barber
    www.makingskincare.com
    www.learncosmeticformulation.com (free online course)
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  • PerryPerry Administrator, Professional Chemist
    Your thinking is correct. 

    If your powder is 10% of the weight of your formula the density of it doesn't matter. So in a 1000g batch you would us 100g of your ingredient 
  • BobzchemistBobzchemist Member, PCF student
    Bulk density only matters when calculating the fill weight of a product. 

    All formulations should be measured by weight only, which makes the density of any ingredient entirely irrelevant. Whoever told you to use bulk density in formulation either has several screws loose or was playing a cruel trick on you.
    Robert Zonis, Sr. Formulation Chemist, Beaumont Products "All opinions and comments expressed are my own, have no relation to Beaumont Products, are fully copyrighted, and may not be used without written permission."
  • CarlJenCarlJen Member
    edited July 2015
    Excellent thank you Perry and Bob for clearing that up.

    MakingSkincare the powder was Colloidal Oatmeal and there are a few other liquids in the formula but i just needed to get my head round the need or not need for the bulk density issue.
  • BobzchemistBobzchemist Member, PCF student
    Density is the ratio of weight to volume, and is usually compared to water as a standard.

    If you are formulating by volume (as if you were cooking, for example) then density and/or specific gravity would be a concern - as in, what is the weight of the ingredient in a tablespoon full?

    When you formulate by weight, everything becomes simpler. You need to put 10 grams of an ingredient into your batch - it doesn't matter if that 10 grams is a teaspoon-full or a cup full or a gallon-full, you still need 10 grams of it in your batch.

    Bulk density and tapped bulk density are measures of how much weight of a powder can fit into a specific volume. You are formulating strictly by weight, so neither of those factors come in to play.

    Hope this helps.
    Robert Zonis, Sr. Formulation Chemist, Beaumont Products "All opinions and comments expressed are my own, have no relation to Beaumont Products, are fully copyrighted, and may not be used without written permission."
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