This is always an interesting question and there are many “theories” floating around the industry on this topic.
At first glance, everyone looks at the wick for the answer, because that is the most apparent source for the heating and the melting of the wax; to me it starts way before that.
A candle is a system and, like most systems, is made of many parts. In this case wax, wick, dye, fragrance, container and/or shape.
To me, hot throw is primarily the function of the wax and fragrance combination. I have always developed and used wax that have a wide range of carbon distribution and a moderate melt point, ranging from 130 – 140F.
It is important that the carbon distribution of a wax does not have many “holes” in it. By this I mean that it has a complete range for example of C15 – C30 including 15, 16, 17…..29, 30.
My house blend was composed of 130 MP FRP, 140 MP FRP, 180 MP Microcrystalline and Petrolatum. This wide range insured that there were no gaps, and if there was, the petrolatum would fill them in.
When soy came into play that changed the way most people looked at wax. Soy waxes tend to have a real wide distribution, with a few “holes” in it. This is why you see the fat bloom or cauliflower look in some candles. This can be controlled by adding different levels of hydrogenated material (hydrogenation controls the amount of “oil” left in the wax). When you mix partial and fully hydrogenated soy wax it closes some of the holes.
I alway used beeswax for the same reason I used petrolatum; because of its wide distribution. Bottom line, if you have an evenly distributed wax base you are heading in the right direction to create a good hot throw. I may be one of the only people left out there who even think this deeply about this but I feel that prices and competition have led to companies losing sight of making the right product instead of the right price. Then, of course, you need to have a properly developed fragrance. I am not as well versed in the chemistry of the building fragrance but having worked with most of the major fragrance houses in the past, here is my opinion.
This industry, too, has been tainted by the need for price over the need for the right fragrance. When I did development work for Avon and SC Johnson, there was no focus on price, just quality. So I saw first hand the difference between a $25.00 and an $8.00 fragrance. A proper fragrance has top, middle and bottom notes built in. All of these together give the sensory smell of what the label says it is. It is important that these are balanced, if the lighter notes are all made of strawberry then after the candle is burned for 4-6 hours, that layer of wax looses its essence of Strawberry. It is important that all the layers support the top notes.
One of my “favorite” discoveries is that some fragrances have a fecal note..that’s right poop! This added a bottom note that supported the top notes and if balanced wrong just smelled like s@%t, lol. My favorite part, of course, is the wick or, more importantly, how the candle burns. The poor wick always gets the blame; when in fact this is the most stable and purest part of the system. Most wicks are 100% nice clean cotton or other single part material e.g. paper, rayon, etc. A wick can only perform with the fuel that it is being fed. If you put dirty gas in your lawnmower then it will perform poorly.
Ironically I have the least to say about the wick because, in essence, it is a simple machine that, when uninhibited by poorly developed waxes, color, fragrance and containers will ALWAYS perform to its fullest potential. In conclusion, I have found that all of my success in formulating the proper candle consisted of the following criteria:
Proper wax blend (as described above)
Properly formulated fragrance…not just cheap
A wick chosen that, when burned in just the wax base alone is not greatly reduced when dye, fragrance and container are introduced. These sometimes increase the performance; which I consider more of a positive, unless it becomes too hot or uncontrollable.
Proper container shape and size. I feel that the container should contribute positively the melting of the wax pool. The wick alone may not be able to get a full melt pool so the container should also contribute. An improperly shaped container can be as big an influence as an improperly formulated wax or fragrance.
A dye system that does not diminish the wicks potential. So many people “wick up” to beat this. The fact that there is a material in a dye that is non-combustible will not change, it will only burn, turn to black carbon and clog the wick.
Slow and steady wins the race. The best candles I have seen and have made did NOT burn to the edges in the first, second or even fourth hour. Think about it this way. A candle fragrance is delicate and formulated to be released when the wax heated. When a candle burns hot and fast it is burning off the best parts of the fragrance and if it has a 1/2″ or more deep melt pool then you are creating even more modified wax. The idea of leaving “fresh” wax on the sides of the container when burning is two-fold. One, the wax pool is not overheated to the point where the fragrance is burned off and broken down and two, the fresh wax continues to replenish the melt pool with “full strength” fragrance as it melts down from the sides.
So there it is, my thesis on what makes a great candle. Feel free to leave a comment.