My New Fragrance Oil Is More Viscous Than the Previous Lot — Could That Affect Candle Mixing, Wick Behaviour or Fragrance Performance?

Is it really thicker, or just colder?

You tip the new bottle and the oil moves slowly, clings to the neck and leaves a heavier film on the stirring stick than the last lot did. It is a fair thing to notice. Viscosity is one of the few properties of a fragrance oil you can judge by hand, and a real change in it can hint at a change in composition. But no supplier at this scale gives you a number to check it against — CSI product pages publish no viscosity, specific gravity or refractive index for any oil — so your comparison has to be practical and fair.

Fair means the same temperature. Almost every liquid thickens as it cools, and fragrance oils are no exception. A bottle that has just come out of a delivery van at dawn, or has sat on the floor of an air-conditioned room, will pour more slowly than one that has been on a warm shelf for a week. Before you compare anything, stand the new bottle beside your retained old lot and leave both in the same room for several hours — overnight is a sensible suggested starting point — so they reach the same temperature.

If, after that, the difference disappears, you have learned something useful about storage and nothing about quality. If it persists, you have a real observation worth recording.

A goods-in flow comparison you can do in ten minutes

You do not need a viscometer. You need two identical containers, your retained reference and a way of making the comparison repeatable.

These are crude methods, and they are meant to be. They will not give you a figure, but they will reliably separate "the same", "a little slower" and "obviously thicker" when both oils are at the same temperature. That is enough to decide what happens next.

Where a thicker oil can actually change your candle

A viscosity difference only matters if it reaches one of three places: how the oil mixes, how the candle burns, or how it smells. Each has its own check.

The dosing row catches more makers than any of the others. If you dose by volume — reading the millilitre marks on a beaker — a thicker oil's slow drain and a possibly different density both move the real amount away from your recipe. That is one more reason to dose by weight every time.

On mixing, CSI's Eco Soy CSI 400 page gives a concrete instruction: add fragrance at 80–90°C and stir for 2 minutes. That is a sound baseline for that wax. With a lot that is visibly thicker, a suggested starting point is to stir a little longer and then check the pitcher bottom before pouring, rather than assuming the baseline time still covers it. Whatever wax you use, add oil comfortably below its published flashpoint.

Worked example: a thick sandalwood lot and a 5 kg pour

Take Sandalwood, which CSI lists with a flashpoint of 203°C, 0% vanillin and loads up to 10% in soy. Suppose you run 5 kg batches at 8% of total candle weight: 4,600 g of wax and 400 g of oil, giving 25 candles of 200 g.

You measure the oil in a silicone beaker and tip it in. With the old lot you never checked the beaker. With the new, noticeably thicker lot, you weigh the beaker after pouring and find, say, 6 g of oil still coating the walls. That is your own measurement, not a published figure — but it shows the effect clearly.

A drop from 8% to 7.88% is small, and on its own it will not ruin a candle. But it is an unrecorded change stacked on top of whatever the lot itself is doing, and it means any throw comparison between old and new lots is no longer like for like. Fix the method first — tare the pouring pitcher with the melted wax in it and weigh the oil straight in, or scrape and rinse the beaker into the wax — and then compare the lots.

Accept, conditionally release or hold

Put the flow comparison together with a smell-strip check against your retained oil, and the decision usually falls out:

When you ask, be specific. Tell the supplier the room temperature, describe the tilt and drip results, attach a short video and ask whether the formula, a source material or the packing has changed. For CSI, message WhatsApp +91 7397976926; IFRA and MSDS documents are available on request there. Write the answer in your goods-in log next to your own observations.

And stay honest with yourself. A thicker lot that makes a better-throwing candle is still a changed lot; approve it on evidence and note that it differs, rather than assuming the next delivery will match it.

Where this page fits

CSI already has guides that cover parts of this question. This page covers the goods-in check for the question above; these go deeper on the rest:

Three things to buy for this job

Frequently asked questions