Conventional candles – especially the thicker ones – are known for the annoying problem of "tunneling." If the
candle's core isn't allowed to burn long enough after the initial lighting to completely cover its surface with
liquid fuel, then after relighting it, it may only
burn in the center, leaving a ring around the wick and forming a deep, hollow hole filled with
liquid fuel in the middle, where the
flame can also be extinguished. This tunneling of candles can be reduced or even completely stopped by constructing their interior from materials with different melting points in such a way that the
melting point of the material decreases "on average" with increasing distance to the wick in a continuous or multi-stage progression. A favorable
melting point decay profile can be determined experimentally by producing
candle prototypes with different
melting point profiles, lighting them, and measuring how long it takes for the surface of the fuel body to be completely covered with liquid material. Many known
candle-making techniques can be suitably modified for producing the candles according to the invention. For example, in step-by-step techniques such as drawing, dipping, and pouring, one can switch to a material with a different melting point after each step or series of steps. In the known pressing process using a screw extruder or a ram press, additives can be injected into the extruder via a side feeder before the material is discharged, locally altering the material's melting point. Alternatively, several extruders can be operated in parallel, each fed with different materials, and their material streams fed into a shaping "sector die." The cross-section of this die is divided into several sectors, and each individual material
stream is connected for
discharge to the sector whose position in the cross-section best corresponds to the desired melting point profile. The familiar
casting process can be modified by rotating the mold around its central axis, causing the material to settle at the edges due to
centrifugal force. After the solidification of the poured material – which may be accelerated by cooling – this
casting process is repeated with a different material each time until the candle is finished. Alternatively, one can first produce several conventional, slim fuel bodies with different melting points and join them together by pressure to form a fuel body according to the invention.