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Formulation Techniques

This guide covers advanced formulation strategies using soap-calc.

Dual-Lye Recipes

Dual-lye recipes use both Sodium Hydroxide (NaOH) and Potassium Hydroxide (KOH). This is common for: * Cream Soaps: Often 60% KOH / 40% NaOH. * Shaving Soaps: Often high in Stearic Acid with a mix of lyes for lather stability and solubility.

To create a dual-lye recipe:

  1. Set lye_type to "Hybrid".
  2. Add ratio_naoh (0.0 to 1.0). The remainder will be KOH.

{
  "lye_type": "Hybrid",
  "ratio_naoh": 0.40,
  ...
}
* ratio_naoh: 0.40 means 40% of the lye is NaOH and 60% is KOH.

Understanding Superfat

There are two ways to add extra moisturizing oils to your soap.

1. Traditional Lye Discount (superfat_pct)

The most common method. The calculator simply reduces the amount of lye used by the specified percentage.

"superfat_pct": 5.0
  • Pros: Easy, safe margin for error.
  • Cons: You don't control which oils are unsaponified; the lye reacts with whatever it finds first.

2. Superfat Oils / Post-Cook Oils

In Hot Process (HP) soap making, you can add specific oils after the saponification cook is complete. These oils remain 100% intact as moisturizers.

To use this feature: 1. Set base_oil_weight instead of total_oil_weight. This fixes the weight of the oils being cooked. 2. Define "Superfat Oils" in your recipe (future feature implementation dependent, currently handled by manually adding oils to notes or specific "post-cook" stages if supported by your process workflow).

Note: In the current version of soap-calc, superfat_pct applies a lye discount across the board. True "post-add" handling varies by process (CP vs HP) and is mechanically a process step rather than a different math calculation, as the total unsaponified fat is the same.

Scaling to Molds

If you have a specific mold, you can calculate exactly how much oil you need to fill it.

Formula: $$ \text{Total Oil Weight} = \text{Volume (cm}^3) \times 0.40 \text{ (approx factor)} $$

  • Wait, soap-calc uses a density of 0.692 g/cm³ for oils.

To calculate volume: $$ \text{Volume} = \text{Length} \times \text{Width} \times \text{Height} $$

Example: A mold is 10cm x 5cm x 7cm. $$ \text{Volume} = 350 \text{ cm}^3 $$ $$ \text{Oils Needed} = 350 \times 0.692 \approx 242 \text{ grams} $$

You can use soap-calc scale to resize your favorite recipe to this new weight.