Lush Lab Shop — Cold-process soap and small-batch | lushlabshop.com
A finished true-soap bar reads pH 9–10 on a strip, and a fully cured, wrapped bar keeps 6–12 months stored below 25 °C away from direct light.
The strip test takes under a minute. Wet the bar, work a light lather with wet hands, press a pH strip into the lather, and compare against the card. True cold-process soap finishes at pH 9–10; that alkalinity is inherent to soap and is not a sign of excess lye.
Context matters when reading the number. Syndet cleansing bars — synthetic detergent products — are formulated at pH 5–7, so a 'soap' that reads in that range is a syndet, not a mild cold-process bar. And a cold-process bar reading clearly above 10 after its full 4–6 week cure points back to the lye calculation: recheck the saponification values and the 5–8% superfat before using the batch.
On narrow screens, swipe or scroll the plate sideways.
Test only after the cure has run. During the first weeks the bar is still losing water, and early readings say little about the finished product; the schedule on the cure-times page sets the testing window at week four to six, or six to eight for Castile.
Once the bar passes, wrap it and put it away cool and dark. Below 25 °C and out of direct light, a wrapped bar keeps 6–12 months; heat speeds rancidity in the free oils left by the superfat — the dreaded orange spots — and light strips both color and scent.
Scent sets the practical limit more often than structure. Essential oils, dosed at 2–3% of oil weight — about 20–30 ml per 1 kg of oils — fade faster than fragrance oils, so an essential-oil bar is best used early in its 6–12 month window, while a fragrance-oil bar usually holds its scent toward the end of it.
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