Can I Mix Two Different Lots of the Same Soy Wax in One Production Batch or Should I Qualify Them Individually First?

Two very different reasons to blend

Makers blend wax lots for two reasons that look identical from the outside and are opposite in intent. The first is consistency: you hold two lots that have both passed goods-in, and by using them at a fixed ratio across a season you narrow the small swings you would see if you ran one lot and then switched abruptly to the next. The second is concealment: one lot is slightly off, or has never been tested, and blending it into good stock makes the difference hard to notice.

The first is a legitimate production decision. The second is a quality decision that has been skipped. The test that separates them is simple: would you have released the lot on its own? If yes, blending is a consistency tool. If no, or if you do not know, blending is a way of not finding out.

This is why the goods-in order matters. Qualification comes first, lot by lot. Blending, if you choose it, comes after both lots have an approved status on their labels.

Qualify each lot on its own first

Before either lot enters the melter together, each needs its own goods-in record. For a lot that has been in production for months, that record already exists. For the new lot, run at least a screen against retained old-lot wax: appearance in daylight, odour of a melted sample, melt and set observation, and a finished-surface check on a small puck. If anything differs, the new lot goes to a paired candle test before any blending decision.

Worked example: 6 kg meets 9 kg

A maker has 6 kg left of CSI 468 lot 1, which has run cleanly for two months, and 9 kg of lot 2 from a new delivery. She pours 200 g candles at 8% load, so each candle takes 184 g of wax. Lot 1 alone makes 6,000 ÷ 184 = 32 candles. Lot 2 alone makes 9,000 ÷ 184 = 48 candles. Blended, 15 kg makes 15,000 ÷ 184 = 81 candles (each figure rounded down).

Now imagine lot 2 has a problem that only shows up after a few weeks on the shelf, such as heavier frosting. If she had kept the lots separate, the problem is confined to 48 candles, and the 32 lot-1 candles are clean evidence of what normal looks like. If she blended before qualifying lot 2, all 81 candles are implicated, the frosting may be milder and harder to attribute, and she has no unblended lot-2 candle to show the supplier.

The table shows the trade honestly. Blending buys a smoother run if both lots are good. It costs traceability and multiplies exposure if one is not. So qualify lot 2 first. If it passes, a 40:60 blend is a reasonable way to finish lot 1 without a visible step change. If it fails, lot 2 stays in quarantine and lot 1 carries on alone.

When blending genuinely helps

There are situations where a planned blend is the better choice. A maker who sells one hero candle all year and buys wax monthly can see small step changes in top finish or throw each time a lot runs out. Blending the tail of each lot into the start of the next at a fixed ratio turns a step into a slope, which customers are less likely to notice. Another case is a lot that passed comfortably but sits at the edge of your normal range, for example a touch firmer, where a planned blend with a lot at the other edge brings production back to the middle.

In both cases the lots have passed, the ratio is written down, and the reason is recorded. That is what makes it a production decision rather than a cover. It is also worth noting what blending does not do: it does not change the wick your formula needs if both lots are within range, and it does not rescue a lot that fails on odour, colour or contamination, because those defects carry straight through into the mixture.

What a blend costs in traceability

A blend is a new material in your records. It needs a name, such as 468 blend L1:L2 40:60, written on the melter log and on every batch sheet it feeds. Keep a small retained sample of the blend alongside the retained samples of each lot; the quantities you keep are a suggested starting point, and a few hundred grams of each usually covers a later comparison.

If a customer complaint arrives, that record lets you test three things side by side: lot 1 reference, lot 2 reference and the blend. If the blend behaves like lot 1, the lot is probably not the cause. If it leans towards lot 2's behaviour, you have a lead to take to the supplier. Without the separate references, you have only the blend and a guess.

A blending rule you can write down

The following rules are suggested starting points to validate in your own workshop, not a standard. Adapt them, then keep them the same from season to season so that your records mean something.

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