Candle Wax Shrinkage
Questions
related to wax shrinkage are the most common of all candle
making questions. Shrinkage is referred to by many terms
including wells, cavities, sink holes, and shrink voids to
name a few. Although shrinkage can be frustrating at times,
it can be reduced under some conditions.
Causes
Like most materials, wax expands when heated. In the process
of cooling it shrinks back down to its original volume. This
shrinkage usually causes a void down the core of the candle,
as well as shrinking away from the mold (allowing it to be
removed more easily). Generally the larger it is in
diameter, the larger the void will be.
Basics
During the cooling process, holes should be poked
alongside the wick. This will help prevent the shrinkage
from distorting the wick, and release trapped air bubbles.
On container candles it has the added benefit of relieving
some of the stress which would pull the wax away from the
glass.
Shrinkage And Molded Candles
As mentioned above, without some shrinkage candles would be
very difficult to remove from the mold. Generally, the
larger the diameter, the more repours will be needed. On
most molds, the bottom is actually the top of the finished
candle. This makes it possible to refill the shrink void
without it being visible (unless turned upside down to see
the bottom). After allowing the candle to cool, just pour
more wax from the same batch into the void. Be sure to keep
the level below the original pour, or unsightly marks will
be visible around the base of the candle. Some dyes tend to
shift color from heat - this can be reduced by allowing the
wax to cool between repours. Allowing the wax to harden
fully between pouring will reduce the number of pourings
necessary to finish the candle.
Reducing Shrinkage In Containers
Shrinkage is more difficult to deal with in glass
container candles since great care must be taken to prevent
the repour from showing. Although I personally find it
easier to just do repours, many find the following helpful
in reducing shrinkage:
- Pour at the lowest possible
temperature. When poured at just above its melt point,
wax shrinks less than when poured at higher
temperatures. This will cause "chatter marks" on the
glass if you don't preheat the molds. This also has the
side benefit of reducing scent loss to evaporation while
cooling.
- Use a low melting point wax.
Generally low MP waxes shrink less than higher MP waxes.
- Add a small amount of hot melt glue
(HMG). I have heard a lot of claims that this reduces
shrinkage, but it is difficult to blend with wax. I
don't recommend it, however those who like to experiment
may wish to try it.
- Petro and/or Vegetable Oil used at
10% to 50% do reduce shrinkage somewhat, but I find they
cause excessive smoke and soot. Again you may wish to
experiment with these and draw you own conclusions.
- If shrinkage is minimal, a heat gun
or small torch can be used to "flow out" the top
surface.
Summary
Shrinkage is a fact of life for most candle making The
information shown above will hopefully help you deal with
it.
