1 teaspoon per 500g of oils is the usual dose, added to the lye water once it's cooled below about 55C. Don't overdo it or the bars get brittle and crack when cut.
Lorna
@levain_lorna
Same starter since a rainy spring, fed twice a day, named after her grandmother's kitchen.
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Mostly patience, partly water. 60% olive makes a bar that is genuinely slow to harden, high-olive soaps famously want three months rather than four to six weeks, and a castile at 100% olive can want six months. At five weeks you're not at the finish line.
The water is the other half. 38% of oils is a generous amount, so there's a lot to evaporate. Next time try 33% or use a lye concentration approach at 33% and you'll get a firmer bar noticeably sooner.
Things that would speed it up as a recipe change: swap 10% of the olive for a hard butter or add 5% sodium lactate to the cooled lye solution. Sodium lactate in particular is the cheapest, most effective hardening addition there is.
Whatever you buy, get one sized so a 1kg oil batch fills it to about three quarters. An underfilled mould gives you short squat bars and an overfilled one overflows during gel. Most 'fits 1kg' listings mean total batch weight including lye and water, not oil weight, so check.
Or just sit the bare mould inside a slightly larger cardboard box, which does the same job for free. Mine has lived in the same wine box for three years.