How long should your candle take to reach a full melt pool?

How long should your candle take to reach a full melt pool?

That’s the topic of this blog post.

What is a melt pool?

The melt pool is the melted wax below a candle.  After you light a candle, the flame begins melting wax below it, creating a “pool” of liquid wax.

Over time, the pool will grow wider and wider, eventually reaching the edge of the container.

A full melt pool describes the time when the melted wax reaches all sides, but is this a sign of a well-built candle, or does it spell disaster?

The Diameter Rule

Some argue that the diameter of a candle container should determine how long it takes to reach a full melt pool.

One hour for every inch.  This means a full melt pool should form in:

• 1.5 hours for a 1.5” diameter container
• 2 hours & 45 minutes for a 2.75” container
• 3 hours for a 3” container

…and so on.  You get the idea.

The rule of thumb suggests that candles are “good” when their melt pools form at that rate, but there are three major flaws in this reasoning.

Fatal Flaw #1: Safety isn’t based on the melt pool

Container candles are always a fire hazard.

It doesn’t matter how good it smells or how pretty the colors are.

Candles have an open flame, and candle makers need high safety standards to guarantee they aren’t putting their users at risk when they burn them.

This brings us to the first reason melt pools aren’t a good measure of success: candle safety standards don’t care about the melt pool.

From a safety perspective, the industry cares more about heat, container integrity, flame height, and incomplete combustion – not melt pool width.  This is mostly based on ASTM 2417, which includes criteria for testing container candles.

As an industry, building safe candles matters more than building strong-smelling candles.  Even though both are important, if a candle isn’t safe, it doesn’t matter how strong it smells.

Doesn’t the melt pool rate tell us how hot a candle burns?

Melt pools will form faster when a candle burns hot, but the Diameter Rule doesn’t guarantee the candle meets all the safety criteria.

Plenty of candles meet all safety requirements and seldom form a full melt pool.

Fatal Flaw #2: Melt pool timing changes over time

Melt pools are a symptom of the candle’s design: the hotter a candle burns, the faster a melt pool forms.

Throughout the life of a candle, the rate melt pools form changes because the heat-to-oxygen ratio changes.  Melt pools expand faster as the heat they’re exposed to rises.

If a candle is judged “successful” based on the Diameter Rule when it was first created, it may fail later.  Consider the following:

It sounds obvious, but the melt pool grows faster when there’s more heat.  A candle that forms a full melt pool in 3 hours in a new candle may create a full melt pool in 2 hours later in its life.

The time a full melt pool takes to form (if it does at all) is a moving target.

Basing a design on melt pool time is unwise and impossible.

Fatal Flaw #3: Scent strength is barely based on the melt pool size

Melt pools are important for scent throw, but how important?

The argument for having a full melt pool is that it’ll help your candles smell stronger and better.  There’s some truth to this: vapors lifted off a melt pool are thrown into the room by the candle.

But scent throw also comes from melting wax (compared to melted wax).  A candle that melts wax nicely throughout its life usually has a consistent throw, all things considered.

More to the point: the wick selection makes the biggest difference in scent throw.  A properly sized candle balances heat, oxygen, and fuel (wax) to provide its users with a safe and well-performing hot throw.

Almost everything starts with the wick: safety, performance, heat, etc.  Melt pools are just one of many things a wick is responsible for.

Melt pool rates are based on the wick, which is far more important to design correctly because it impacts more elements of a candle’s success.

How long should your candle take to reach a full melt pool?

In short: don’t pay much attention to the time a full melt pool takes to form.

Candlemakers should judge the success of a candle based on safety and performance testing, not how fast the melt pool forms.  Melt pools form at different rates throughout a candle’s life and don’t directly indicate whether the candle is safe to use or performs well.

Following the Diameter Rule – that a melt pool should form at a rate of 1 hour for each inch of its container’s diameter – may result in unsafe candles that burn too hot further into their life.

Instead, judge safety with the industry standard test and the BLO test for hot throw.

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