Bougies et fondants

wax       = V × ρ_solid × fill × vessels     # ρ solid, not molten

of wax:   fragrance = wax × load ÷ 100
of total: fragrance = wax × load ÷ (100 − load)   # it is part of its own total

load of wax   = fragrance ÷ wax × 100
load of total = fragrance ÷ (wax + fragrance + additives) × 100

• Wax manufacturers state maximum fragrance load as a percentage of wax weight: fragrance = wax × load ÷ 100. Expressed as a percentage of the finished candle the same load is fragrance ÷ (wax + fragrance) × 100. — The two conventions differ by roughly a tenth of the load. Always check which one a supplier figure is quoted in.
• Solid paraffin and vegetable waxes have densities around 0.90–0.96 g/mL; molten, around 0.77–0.82 g/mL. A vessel measured by filling it with water gives its volume, which must be multiplied by the solid density to give the wax it holds. — Manufacturers publish a density per grade; use theirs where you have it. The defaults here are a starting point.
• The flash point on a fragrance oil’s safety data sheet is the lowest temperature at which its vapour forms an ignitable mixture. Adding fragrance to wax above that temperature risks ignition and drives off the volatiles that carry the scent.
• Cure is the time between pouring and burning, during which the fragrance binds into the wax matrix. Soy and coconut waxes are conventionally cured 1–2 weeks, paraffin 24–48 hours. — A convention of the craft. There is no published measurement that fixes a cure time for a given wax.