Metal on Metal Corrosion: Why Does It Happen?

Creating the perfect candle is a delicate task balancing art and science. While most candle makers focus on achieving a flawless wax finish and a lovely smelling fragrance, there is a hidden chemical challenge that can ruin the entire batch - metal on metal corrosion.  Whether you are a pro candle maker or someone who loves making candles as a hobby, understanding how the tools interact with your raw ingredients is very important. 

When looking for your candle making equipment, you will need lots of metal tools. Such as melting pots, stirring spoons and thermometers. Placing different metals together especially when heating and highly reactive ingredients can trigger unwanted reactions. Let’s explore why this happens and what you can do to protect your tools. 

Understanding the science

To properly protect your tools, it’s important to know the difference between oxidation and chemical corrosion in candle making. Oxidation happens when a metal reacts to the oxygen and moisture in the air. Chemical corrosion happens when metal rapidly breaks down due to the reaction with a harsh chemical, such as acidic fragrances or chemical wax additives.

Another factor to consider when making candles is the temperature. The effect of high heat on metal containers can weaken their protective coatings. 

Candle Ingredients Reacting with Metal

Many pure essential oils and synthetic fragrances contain aggressive chemical compounds such as citrus acids, cinnamon and vanilla can react with raw metals over time if the barrier is scratched or missing which leads to discolouration.

Why do essential oils react with aluminium candle tins specifically? Aluminium is a reactive metal. Without a strong protective barrier, the natural compounds found in essential oils will bind the aluminum, leading to pitting and scaling. This leaves a dark ring around the inside of the candle. However, not all aluminum candle tins do this if they are protected properly and the tins offered at Tinware Direct have an internal protective lacquer. 

Why Protective Lacquer Matters

Protective lacquer coatings are essential for metal packaging. It is a barrier which prevents direct chemical reactions between metal and its contents, stopping corroding. 

Tinware Direct’s tins and bottles are manufactured with a protective coating, which acts as a barrier between the contents and metal. This prevents staining, metallic marks and corrosion when the packaging is used correctly. 

Problems are most likely to happen if the protective coating is scratched by tools, the packaging is damaged/dented, fragrance oil is spilled around the tin, the container has overfilled, or exposed to temperature changes. 

Fragrance Types That May Need Extra Care

Some fragrances can be more likely to cause staining or a reaction if left in contact with exposed metal. 

• Vanilla, caramel, chocolate or sweet smells.

• Cinnamon, clove and spiced fragrances.

• Citrus fragrances containing acid.

These ingredients are not necessarily unsuitable for metal packaging, they just require correct cleaning and testing is really important. 

Why Are Container Lids Important?

You may not notice any metal corrosion inside the tin, however the spill point areas can become more vulnerable if exposed. 

It’s important to make sure that the metal container is cleaned after filling. Fragrance oil can collect around tin rims or bottle necks during filling. 

When sealing the lids and caps can spread small amounts of oil. Which can then be harmful to metal corrosion. The best practice is to:

• Always wipe away spilled fragrance oil from rims, threads, necks and lid contact areas before sealing.

• Do not leave fragrance oil sitting on the outside of tins or caps.

• Check containers after filling and again before packing.

• Use a clean, soft cloth suitable for the product being handled.

Avoid Scratching The Protective Barrier

The protective barrier works best when the barrier remains intact. So it is best to avoid these:

• Using sharp tools inside or around the container.

• Scraping wicks or stirrers against the container.

• Handle lids and caps carefully to avoid chipping the coating.

• Avoid stacking or moving tins in a way that may cause scratches.

• Keep tins protected during storage before filling. 

Metal candle tins are a popular and practical choice for candle makers. They are lightweight, durable, attractive and suitable for a wide range of candle products. However, as with any packaging they need to be used correctly.

By understanding how fragrance oils, waxes and additives can interact with exposed metal, candle makers can reduce the risk of staining, corrosion and product issues.

Protective lacquer with careful handling, good cleaning practices and product testing all play an important role in creating a reliable finished candle.

At Tinware Direct, our tins and bottles are designed with protective coatings to help support safe and effective use. However, we always recommend testing your chosen wax, fragrance and filling process before committing to a full production run.