Adding fragrance and dye

The last two ingredients, the two that sell the product, and the two most easily wasted.

Late, and pre-mixed

Fragrance goes in near the end, after pH is settled and the batch is at working temperature rather than warm.

Pre-mix it into its solubilizer first, as a separate small blend, then add that blend to the batch. Adding neat fragrance oil to water gives you droplets that never disperse properly however long you stir.

Not into a hot batch, which drives off the top notes and scents the room instead of the product.

The solubilizer does the work

At the level the supplier states for your fragrance load, which is usually a multiple of the fragrance weight rather than a fixed percentage.

Under-dose it and the product is clear on the bench and cloudy within a week, which is the version that reaches customers.

Check clarity after standing, not immediately: a freshly mixed batch can look clear and separate overnight.

And check it cold, because the cold is where an under-solubilized formula shows first.

Dye last

Pre-diluted in water rather than added as a concentrate, so it disperses rather than streaking.

At the lowest level that gives the color, judged against a standard rather than by eye in the vessel: a batch in a large vessel always looks darker than the same product in a bottle.

Keep a color standard and match to it.

Then stop

Mix gently and briefly. Both of these are added at the point where the batch is finished, and extended mixing now only entrains air.

Let it stand until the air is out before filling.

And do not correct the fragrance level by adding more at the end of a batch. That is how a formula drifts upward over a year until it separates.

References