Order of addition

Two batches with identical ingredients and different addition orders are different products, and frequently one of them is ruined.

The order is part of the formula

A formula sheet that lists ingredients without an order is incomplete. The order is process, and process is half of what makes a product reproducible.

A general sequence

Water first, most of it, so everything has somewhere to go.

Chelator and builder next, so hardness is dealt with before the surfactants meet it.

Surfactants, slowly, with gentle mixing. Fast addition entrains air and makes a batch of foam you then have to wait out.

pH adjustment, once the bulk is in and dissolved.

Thickener, according to its own requirements, which frequently means a specific pH or a specific dispersion method.

Preservative.

Fragrance, pre-mixed into its solubilizer, last or near last.

Dye last.

Then the remaining water to final weight.

Why order matters

Solubility. Several materials dissolve readily in water and not at all in a concentrated surfactant solution.

pH sensitivity. A thickener added at the wrong pH never builds viscosity, and adding acid or alkali afterwards does not fix it.

Local concentration. Adding a strong acid or alkali into a small volume creates a pocket at an extreme pH that can destroy a fragrance or precipitate a surfactant before it disperses.

Air. Anything added under high shear entrains it, and a foamed batch cannot be filled accurately.

Recording it

Numbered steps on the batch sheet, with mixing speed and time, temperature where it matters, and the point at which pH is checked.

Written so somebody else could follow it, which is the test of whether it is a process or a memory.

References