Test Burning Candles for Proper Wick Size

This is basically the paper that was included in the Jan/Feb 2013 issue of the Saponifier Enjoy!

Candle makers often talk about test burning candles.. It seems like common sense that a candle maker who sells a product would know how their candles burn.  It is a bit surprising that few candle makers actually have a system that will generate repeatable results.  A lot of candle makers have different ideas about test burning.  But what exactly does “test burn” mean and how do you go about doing that. These guidelines are created to help better understand what a productive test burn involves in order to achieve reproducible results.  The important thing to take away is that repetition is needed. 

Simply put, the test burn is used to understand how a candle burns. Pillars, containers, votives and tea lights all burn differently even if the same wax, wick and additives are used. Size (diameter and depth) and container (metal, glass or none) greatly affect how each candle will burn. Each candle type must be test burned to insure accurate performance. For instance, the taller the container candle, the greater the trapped heat factor. Trapped heat is the heat that is trapped in the jar as the candle burns down.  The further down the candle burns the more heat that builds in the jar. Containers will have more trapped heat and tea lights will have the least. This is important to understand.  A candle that seems to burn well at the beginning of its life could become a flamethrower as the wick nears the bottom of the candle. It is also important to understand, as the candle burns down the diameter burns out.  This generates more trapped heat.  This will be discussed later in the paper.

So, when evaluating your wicks for proper burning in candles you will want to do the following;

Do your research!  I can’t say this enough.  If you plan on selling a product you should know that product!  Here are some things to consider when test burning candles.

 
Many wick sizes and types.  When you have an entire line of candles it is usually not a good idea to try and use just one size or type of wick. There are many different families of wick on the market today and each type is designed to perform best under specific circumstances. Braiding tension, type of material used, possible inner core or flame retardant treatment all contribute to the burning properties of the wick. Families of wick are HTP, CD, CDN, PK, RDH, Eco, square braid, etc. Each type of wick should have application information. When testing choose many wick families that you think will work best with your candle and go from there. 

All wicks are not the same. When you test 5 different wicks from different wick families that are supposed to perform well in the same wax and burn the same diameter they will not perform the same. That is why test burning is so important.  Different families of wick burn better in different wax/scent/dye combinations. For instance,  HTP 1212 may work wonderful in a 4” EL soy container jar with Serendipity scent and Scarlet Fever dye crystals but it will fail when you use it in a 4” EL container jar with Patchouli Dreams and Midnight dye diamonds.

All waxes are not the same. Just because two different waxes are 100% soy does not mean that they will burn the same, have the same scent throw abilities or even the same dying abilities. The soybean can be taken apart to form many different compounds. I’m sure that you are all familiar with tofu or soymilk. Both of these are from the soybean. Now can you see burning either one of them? Some waxes will be easier to burn then others.  Some will have better scent throw then others.  And some will change their burning properties whenever something is added. 

All fragrances and additives are not the same.  These are the factors that will have the most variability.  When testing you will want to hold them constant as you test for wick size.  Use the manufacturers recommended about of scent for your testing.  Just because a wax can hold 10% oil doesn’t mean that you should use that much!  In fact, sometimes using too much scent can “lock up” the scent or change the scent as it is burning.  Also, super concentrated scents need very little scent because there are more raw materials in their composition and less filler.  Filler is cheap and will often be used in inexpensive scents to keep the price of a pound low.  But you just end up using more oil to get good hot scent throw.

After you have picked out wicks, wax, additives and scent it is time to start testing.

Burn multiple candles with the same wick.—Another important component of testing is to make sure that you can duplicate your results. Make sure that you have at least two of all of your wick sizes/types that you are test burning. This helps to insure that your results are accurate. Any number of problems may affect an individual wick. You may get an unreliable burn if the wick was not primed correctly, something got into your candle, the wick incorrectly labeled, braiding tension was faulty, etc.   Thus, if you have two or more of the same wick/wax/scent/dye combinations and they are burning the same you can be more assured of the accuracy of your results. Other things to be cautions of while test burning are improper wick priming, trimming the wick too short, not trimming enough, pigment in the color clogging the wick, drafts, etc.

Example-- Lets say we want to test a new scent.  We test our 4” diameter jars with the EL soy container wax.  For this one scent we use about 6 different families of wick and many different sizes. In all we have about 20 – 24 jars burning at a time.  That is 10-12  jars with the same wax and scent but with a different wick.  Then we do a duplicate of each. For example, 2-CD18, 2-CDN18, 2-CD20, 2-CDN20, 2-CD22, 2-CDN22, 2-#2 square braid, 2-#5 square braid, 2-HTP 1212, 2-PKN15, 2-PKN20, 2-RDH 15, 2-RDH 17 

Also, make sure that you burn all of the candles at the same time. This way you will be able to see how each is doing compared to the others throughout the entire test. Remember not to put the candles too close to one another or their heats may affect each other.  Put about 3" apart.

Burn the entire candle. Candles burn differently throughout their life. As a candle burns down vertically it will burn further out horizontally. This is due to the heat of the flame creating more trapped heat as the candle burns down. Containers hold this heat more drastically then pillar candles. This trapped heat helps to burn the sides of jars and pillars. There is little trapped heat until the candle burns about 1” down. It could take many hours to get to this point.  I will call this zone one. When the candle is about 1” down the flame will start to melt more of the “hang-up” on the sides of the candle. This will be zone two. As the candle burns down and the flame nears the bottom of the candle the trapped heat is the greatest. This will be referred to as zone three.  If the wick is burning too hot it can cause excessive sooting or it can break glass.

How the candle should burn. The general rule of thumb is that for every inch in diameter that a candle measures, it should take about 1 hour to burn. A three-inch diameter candle should take about 3 hours to burn as far as it is going to burn. The burning diameter will expand as the candle burns down. Remember the trapped heat? You don’t want your candle to burn all of the way out to the edge until the candle is about 1” down. Otherwise it will be way too hot by the time it gets to the bottom of the candle. This notion is generally held mostly for containers.  There are some exceptions to this rule.  Very shallow containers (less then 2” deep) should get full melt pool on the first burn. Pillars on the other hand will start to consume their edges once they start to get about 1” down. If they are too hot they will blow out the sides.

The following details are for how a container candle should burn. Pillar candles burn the same after the first inch.  Whereas container candle have different burn zones.

In the first zone the candle should feel warm on the top portion and should burn out to within ¾” – 1” from the edge within it’s given time period. (One inch per hour).   When the candle reaches the second zone the top wax “hang up” will start to melt.  When the candle has reached it's full burn time (2 hours for a 2 inch diameter, 3 hours for a 3 inch diameter candle)   in zone two it will leave very little wax on the edges. The melt pool may get as deep as about ½”. In the third zone the side hang up will completely melt within it’s proper burn time (one inch per hour of diameter) and the melt pool may get as deep as 1”.

The deeper the candle the more exaggerated the zones. In a 6” deep candle the first zone may extend down 2” or more.   Different depth candles will have different zone depths and it will take some experiments on your part to determine where the transitions occur. 

Record your information—I can’t say this enough.  Keep very detailed information on everything that you do to make your candles and while test burning. You will then be able to reproduce them. You won't be able to "remember" all the steps.

 Even the best minds get a bit hazy when dealing with a bunch of candles.

Some of the information that is important to note when pouring your candles; Room temperature, humidity level, temp you add your scent and additives, temp you pour your candles, amount of dye, amount of scent, amount of wax, and amount of additives.

Factors that should be recorded when test burning. 

1)      Initial weight of candle (you can weigh the jar with the candle in it since you will be using the change over time to determine how your candle burns)  

2)      Weight after certain time periods (we do ours every ½ hour) 

3)      Flame height 

4)      Melt pool depth at different times, melt pool diameter at different times, when does the candle get a full melt pool, when do you have to trim the wicks, is the candle smoking (sooting) and does the jar get excessively hot.

5)      Another good thing to look at is first ignition. (How long does the flame stay up when it is lit for the first time at the beginning of every burn?   If more than one minute the wick capillary action is probably too strong. Steadiness of flame is another factor to study.  (Does it bounce around?) The more stable the flame the less soot and mushrooming. 

6)      And finally record the final weight of the glass when the candle has fully burned.

You may find in your own testing that there are other factors that you may want to include. My list is by no means all-inclusive.

Determining the winner.—With all of your testing information it is much easier to determine the winner. Which one did the best overall? You now have plenty of information to compare to wick manufacturer specifications and your own guidelines.  Little soot, good melt pools, jar not too hot, short initial burn flare-ups, no bouncing flames, flame height the correct size (check manufacturer’s guidelines), few wick trims needed, etc.

After we have determined which wick to use we make a couple of candles and give them a torture test.   The torture test is to let them go all day, about 6-10 hours.  We can then see what they will do if a customer lets them burn too long.  If they don’t need an excessive amount of wick trimming and the jar doesn’t get super duper hot I feel much more confident about my results. After a good torture test we then alternate between normal burns and torture burns.  A normal burn is when you give your candle one hour of burn time for every inch of diameter. So a four-inch candle gets four hours. You will notice that the candle will consume the first inch of diameter much faster then the last inch. That is why it needs the full burn time for a good test. Your candle may get all of the way out to 2” (for a 3” diameter candle)  in the first 30 minutes and then putt along for the next 1.5 hours to reach the outer edges.  The closer the flame is to the wax the quicker it will melt and the further away from the flame the longer the wax will take to melt.

The final burn—One last step. Now that you have determined which wick that you want and given the final torture burns it is really a good idea to make up two more jars with your chosen wick, wax, dye, scent combo and burn them like it says on your instructions. Again, one inch for every hour the candle burns. You can go a couple of extra hours some days but don’t give them any torture tests for this one. Then when the candles are finished burning evaluate how they did. If they burn out nice and clean you are ready for production. If you have problems it is back to the drawing board. Look at all of the components and see what you did differently. You may have even mislabeled something.  You may be tempted to skip steps and cut corners because of all of the materials involved but remember you are creating a product that someone will be burning in their homes!  You should really know the candles that you are selling.

Enjoy the trip-- Try not to feel bad if you do need to spend more time on evaluations and further burns. This is what being a candle maker is all about. If everyone could make a candle there wouldn’t be any reason for candle makers. And don’t forget that testing and knowing your candle will really set you apart from hundreds of other candle makers out there.  Which in turn will help you sell your candles!  Think of all of this testing as an investment.

One last word on test burning. Legal issues. Insurance isn’t enough. If you document the fact that you know how each one of your candles burns you will be in a much more stable place if there is ever a legal question. Keeping your test burning records along with giving burning instructions make it much more difficult to indicate negligence on your part. How could you be negligent if you took the time and effort to know your candles!  The burden of proof them falls on the customer to show their burning records.

And most of all have fun! I hope that you enjoy a little of the science of candles as well as the aesthetics.

Lyschel Bersch

Owner- Candle Cocoon, llc