Glass candle holders are a popular choice among candle enthusiasts due to their aesthetically pleasing appearance. But, is all glass safe to use with candles? In this post, we will explore the topic of whether or not all glass is safe for candles and provide tips on how to choose the safest glass candle container.
Not all glass is not safe for candles. Glass must be heat-resistant, strong enough to withstand thermal shock, and non-porous to be safe for candles. Containers made from borosilicate glass and chemically tempered soda-lime glass are excellent options. Glass that does not meet these criteria can crack or break easily.
Did you know that some types of glass can actually be dangerous to use? That is why when choosing a glass jar for a candle, it’s important to consider the chemical and physical properties of the glass. Different types of glass can affect how a candle burns, and some are safer than others. Here’s all you need to know.
Checklist for Choosing the Safest Glass Container for Candles
Whether it be making or burning candles, the type of glass container you use is just as important as the wax and wick. The wrong glass can crack or even shatter, which can be dangerous if the flame gets near your skin or any combustible object.
So, what should you look for when choosing a glass container for your candles? Here are some vital criteria to consider.
- Resistance to Heat
If the container that holds the wax is not heat resistant, then it can crack or even shatter as the temperature rises due to the lighted candle. The table below specifies the heat resistance and other chemical properties of the two most common glasses used in manufacturing jars:
|Type of Glass||Softening Temperature||Maximum Thermal Shock Resistance Range||Coefficient of Thermal Expansion|
|Borosilicate Glass||1650°C (3000°F)||165°C (300°F)||≈3 × 10−6 K−1 at 20 °C|
|Chemically Tempered Soda-Lime glass||573°C (1063°F)||Soda-lime glass: 270°C (518°F)||9 ppm/K, ~100–300 °C (212–572 °F)|
The softening temperature is lower than the melting point, which is the temperature at which the glass completely liquefies. Because of this, the glass can be worked into the desired shape while it is still in a softened state. However, once the glass reaches its melting point, it will no longer retain its shape.
The melting points of different types of wax used in candles lay in the range of 45°C – 82°C and seen above the softening temperatures of the borosilicate glass and chemically tempered soda-lime glass are considerably higher. However, this does not guarantee they are unbreakable. Proper caution is necessary when using candles in glass jars.
- Resistance to Thermal Shock
The thermal shock resistance of glass refers to its ability to withstand sudden changes in temperature without shattering.
When heated, glass expands slightly, and when cooled, it contracts. Ordinary glass can crack when exposed to extreme temperature changes. This is because the layer of the container in contact with heat expands slightly, whereas the opposite layer in contact with cooler temperature does not, thereby resulting in a temperature gap.
If the glass cracks, it can disrupt the flow of liquid wax and cause the candle to extinguish itself. In addition, cracked glass can be dangerous, as hot wax can spill out and cause burns.
That’s why thermal shock-resistant glass is so important for candles – you want a glass that can withstand both the heat of the candle flame and the cooler temperature of the room. This type of glass is usually thicker than regular glass, and it has a lower thermal expansion coefficient.
The coefficient of thermal expansion (CTE) is a measure of how a material will expand or contract in response to a change in temperature. For example, the low CTE of borosilicate glass (almost 1/3rd of the CTE of soda-lime glass) is also responsible for its unique ability to withstand sudden temperature changes.
The glass used for candles should be non-porous so that it doesn’t absorb the wax as the candle burns. If the wax is absorbed, it can create a larger base, resulting in an uneven flame.
A porous glass will also allow the fragrance and color of the candle to be absorbed into the container, eventually becoming “scented” and no longer ideal for use with candles containing other scents or colors. Non-porous glass is clearer, which allows the light of the candle to shine through uninterrupted.
Finally, as the wax is burned away, it will leave behind a sooty film on the inside of the glass that can be difficult to clean.
How to Tell if a Glass Jar is Heat Resistant/Tempered?
Now that we have established the importance of glass jars being heat resistant, the next step is to be able to identify this property.
Tempered glass is created by heating the glass to a high temperature and then cooling it rapidly. This process makes the glass four to five times stronger than regular annealed glass. However, tempered glass is not completely shatter-proof; if it is damaged, it will break into small, harmless pieces rather than sharp shards. But this is not one way to check its heat-resistance status!
Below is a short guide on how to tell if a candle glass jar is tempered or not:
Step 1: Check the Edges
Tempered glass will have smooth edges. One of the reasons is that it undergoes a process called “heat strengthening.” During heat strengthening, the glass is heated to just below its melting point and then cooled very rapidly. This also makes the glass harder and more resistant to breakage.
Step 2: Check the Label
One way to tell if a glass jar is heat resistant is to look for the “heat resistant” symbol. This symbol is usually printed or sandblasted on the bottom of the jar. It will spell out the name of the manufacturer, the Consumer Product Safety Commission (CPSC) standards, and the symbol.
If the jar does not have this symbol, it is necessarily not heat resistant, but it is best to err on the side of caution and assume that it is not. In this case, we look for other signs.
Step 3: Check for Imperfections
The manufacturing process can sometimes result in small imperfections in the glass. These imperfections are relatively harmless and do not affect the strength or safety of the glass, but they can be visible to the naked eye. In most cases, they will appear as dimples, warping or blending on the glass.
These imperfections are a good thing, as they indicate that the glass has been properly treated and is less likely to break when exposed to high temperatures.
Step 4: Use Polarized Lenses
Tempered glass will typically have shaded or dark spots or lines stretching across its surface, which are created by the machine rollers during the tempering process. This effect is most easily seen in sunlight. So, if you put on a pair of polarized sunglasses and look at the glass, you should be able to tell fairly easily whether it’s tempered or not.
5 Safest Glass Containers for Candles
For many people, candles are an essential part of creating a relaxing ambiance. However, in recent years, there has been an uptick in reports of candle fires and injuries associated with candles. As a result, it is important to choose your candle containers carefully.
The following six types of jars are made from either borosilicate glass or chemically tempered soda-lime glass and can be used with candles:
1. Mason Jars
Mason jars are a great option for candles because they’re made of thick glass. This means they won’t shatter easily under heat and are less likely to break if knocked over. Mason jars also have a wide mouth, making them easy to fill with wax.
2. Apothecary Jars
Apothecary jars are similar to mason jars, but they’re usually taller and thinner, giving a vintage look to your decor. They’re also made of thick glass, so they’re just as safe as mason jars. Apothecary jars can be a bit more difficult to fill, however, because of their narrow opening.
3. Hex Jars
Hex glass jars can withstand high temperatures without breaking or shattering. In addition to being safe, hex glass jars also lend a stylish look to any candle display.
4. Tureen Jars
Tureen jars have a wide opening and a stable base, making them safe to use with a small candle.
5. Vibe Jars
Vibe jars are usually broader at the base, giving them a sleek look which makes them a great addition to any home décor. The mouth is wide enough to pour in wax if you are making candles.
What Not to Use as a Candle Container?
Some glass objects are not suitable for use as candle containers. In addition to the material, the size and shape of the holder should also be considered. Here are some objects that should not be used as candle containers:
- Glass Vase
Glass is a poor conductor of heat, meaning that it can take longer for a candle to melt the wax when it is placed in a glass vase. This can result in an uneven burn and produce unsightly black soot on the inside of the vase. Glass vases are not heat resistant and can crack or break when exposed to extreme changes in temperature. When this happens, the hot wax can cause the glass to shatter, potentially causing injury.
- Wine Glass
One should never put a candle in a wine glass. For one thing, the heat from the flame can cause the glass to crack or shatter. In addition, wax can be difficult to remove from the inside of a wine glass, and it can also leave behind an unpleasant smell. Finally, if the candle is not placed properly, it can drip wax onto the tablecloth or table surface. While candles can add a touch of elegance to a dinner party, it is usually best to avoid using them in wine glasses.
- Drinking Glass
While they may seem like attractive candle containers, drinking glasses can be quite dangerous. The heat from the flame can cause the glass to crack or break, and shards of glass can easily cause injuries. The flame can also cause the glass to become hot to the touch, making it a potential fire hazard.
If you’re not sure whether a glass jar is tempered, check with the manufacturer before purchasing or check for the tell-tale signs of the tempering process of the jar.
How Long Should You Let a Candle Burn in a Glass Jar?
When it comes to burning candles, there is such a thing as too much of a good thing. While it might be tempting to let a candle burn for hours on end, it is not good for the candle or your home. Here are a few reasons why you should not let a candle burn for more than 4 hours:
- Prolonged burning can cause the wick to become misshapen. This in turn can cause the flame to flicker and produce soot, which can discolor the glass jar and surrounding area. In addition, a misshapen wick can cause the flame to become unstable, increasing the risk of fire.
- As the candle continues to burn, more and more wax is vaporized and drawn up into the flame, where it is consumed. However, if a candle is allowed to burn for more than four hours, there is a risk that the entire pool of liquid wax will be vaporized. This can cause the wick to “mushroom” as it draws in air from around the flame. It can also cause the heat of the flame to increase, potentially leading to a fire.
- Letting a candle burn for too long can release harmful particulate matter into the air. These chemicals can be hazardous to your health. A study revealed that these released particulars harmed mice as much as diesel fumes.
- Extended burning depletes the wax supply. Not only does this shorten the life of the candle, but it can also cause the flame to become weaker and less visible.
So next time you light a candle, be sure to blow it out after 4 hours. If you wish to relight it, let the candle cool down for two hours first.
How Dangerous is a Candle Fire?
A candle is an often used household item, but many people are not aware of the dangers they pose. Each year, thousands of house fires are started by candles, resulting in millions of dollars in damage and, tragically, hundreds of deaths. The vast majority of these fires could be easily prevented with a little bit of care and attention.
According to the National Fire Protection Association, candle fires accounted for an estimated 7,400 of all reported home structure fires from 2015 to 2019.
On average, there are 20 candle-related home structure fires reported per day. These fires resulted in an annual average of 90 civilian deaths, 650 civilian injuries, and $291 million in direct property damage.
Candle fires are particularly dangerous because they can start quickly and spread rapidly. A small flame can easily ignite a nearby curtain or piece of furniture, causing a devastating house fire. In just seconds, a room can fill with thick smoke and intense heat, making it difficult to escape. The risk of smoke inhalation is high in any fire, and candles are especially dangerous in this regard due to the fact that they often contain toxic chemicals.
Bedrooms were the leading area of origin reported in these fires. The graph below highlights the seriousness of this issue:
The research reported that the first items to be ignited were mattresses, furniture, curtains, and cabinetry, followed by decoration, paper, upholstered furniture, and clothing. In 16% of these fires, the candles were left unattended due to sleep, drug, or alcohol impairment.
What’s more, candles can easily tip over, causing the hot wax to spill onto nearby surfaces. As a result, it’s important to be careful when using candles and to make sure they are placed in safe, stable locations. With some basic precautions, you can help to prevent candle fires in your home.
Vital Precautions to Take When Keeping Candles in Glass Containers
When using candles in glass containers, some vital safety precautions must be taken to avoid any accidents. Here are the most important ones:
- Always use a candle holder that is stable and won’t tip over easily.
- Never leave burning candles unattended. If you have to leave the room for any reason, be sure to extinguish the flame first.
- Keep candles away from flammable materials such as curtains, furniture, or paper.
- Trim the wick before each use to prevent excess smoke and soot build-up. The National Fire Protection Association recommends that you trim the wick to ¼ inch before lighting the candle. This helps the candle to burn evenly and prevents the flame from getting too hot.
- Don’t allow the flame to come into contact with the sides of the glass container; this can cause the glass to heat up and break.
- Extinguish candles when they reach the end of their burn time. Don’t try to extinguish them by blowing them out; use a snuffer instead. Snuffers are designed to extinguish candles without damaging the wick or spilling wax. To use a snuffer, simply place the domed end over the top of the candle and wait a few seconds for the flame to be extinguished.
- Never move a burning candle; wait until it has cooled down completely before doing so. f you try to move a lit candle, you run the risk of spilling hot wax or knocking the candle over and starting a fire.
- Keep the containers out of reach of children and pets.
Q. Is Concrete Safe for Candles?
- Concrete is durable and heat-resistant. However, you should keep in mind that concrete is not completely non-porous. This means that it can absorb some of the fragrance from your candles, which can affect the smell of future batches of candles. Concrete can also be tricky to clean, so you may want to choose another material if you plan on frequently changing your candle scent.
Q. What Are the Most Common Reasons for Candle Glass Breaking?
- There are two main reasons for this. First, if the wick is not centered, it can get too close to the side of the glass and cause the glass to break. Second, if the flame gets too close to the bottom of the glass, it can also cause the glass to break. In both cases, the heat from the flame causes the glass to expand and eventually break. To avoid this, make sure that the wick is centered and keep the flame away from the sides and bottom of the glass.
Q. What Objects Can I Put in Candles for Decoration?
- Just about any small, non-flammable object can be used to add a personal touch. For a unique look, try using dried flowers, herbs, or spices. You can also use small beads, shells, or stones. If you want to add a bit of color, consider using crayons or markers to draw directly on the candle. Just be sure to use a non-toxic wax and keep the decorations away from the flame. With a little creativity, you can easily transform a plain candle into a work of art.
As a general rule, any glass that is heat resistant and non-porous is safe to use with candles. This includes materials like borosilicate and chemically tempered soda-lime glass. Whether being used for decoration or to set a peaceful ambiance, candles should be used with precautions. By following the above safety tips, you can help make sure that your next candle-lit evening is enjoyable and fire-free.