Poor glass adhesion can also be described as wet spots on the side of the glass vessel and looks like a ‘wet’ appearance in parts. It’s worth noting that this is very common when making candles in glassware, mainly with clear vessels whereby it’s easily visible, and natural waxes can also be more prone to it. If you do some research, you will find even some of the most expensive soy wax candles, on the market, have the same result. You are certainly not doing anything wrong if you do see some wet spots and it most certainly will not affect the way your candle burns.
The reason this happens is basically due to the minor shrinkage that occurs when the wax is cooling and the minor imperfections on the inside of any glass surface. The wax will pull away from the glass in some areas and be left stuck to the side in others.
As mentioned before, by no means is poor adhesion a product problem. However, it is acknowledged that visually the candle does not look perfect, and you may have customers who would prefer not to have it. So, what are the options? Well, the most obvious solution is to use frosted glass instead of clear as glass adhesion is not as noticeable. However, most people do enjoy the clear glass vessels and clear vessels do add that element of class to a candle. It’s also a fact that clear vessel sales outnumber frosted sales by over 2 to 1. So, let’s look at some other solutions for preventing poor adhesion in clear vessels for candle making with soy wax.
Preheating your vessels prior to pouring has worked well for a lot of chandlers. Depending on your manufacturing output, requirements will vary on what process you use. You can easily test this by using a heat gun to give your glass some initial heat, which reduces the temperature differential when you pour in the warm liquefied wax. You could also preheat your vessels in the oven first, say on a tray before pouring. The vessels generally don’t need a lot of heat, so we are not talking about making the glasses hot to touch. Some larger scale manufacturers will run their glasses through a preheating chamber on conveyor belts prior to pouring and they say this does eliminate a lot of container adhesion problems.
However, poor adhesion can be really hit and miss. One minute you are getting great results and the next batch you have different results. Like any testing, though, it’s essential to document your pouring temperatures and ratios every time you make a batch of candles, so you can easily go back and troubleshoot and work out what was different and find out exactly what you did last time you poured. In some instances, slowing the rate of cooling by allowing your candles to set in a much warmer workspace may also help, around 21°C – 23°C (69°F – 73°F)
We hope this gives you some insight into the widespread results from making candles in clear vessels and the sometimes-intricate nature of pursuing the goal of making perfect candles.