Rock Fuser

A rock fuser is a magical device used by the inhabitants of the city of Understone in the Depths to cause rock to metamorphose into a nearly unbreakable form through the application of extreme pressure and heat.

Appearance

The exact form of these devices varied by their intended use and desired decorative patterns, if any. The simplest form, such as the device found by Melodia Silvereyes' ill-fated expedition, is comprised thick sheet of stone with magical runes carved into it on one side and a flat metal panel mounted on the other. Crude examples of the device might use a flat iron panel and simple carved limestone, but more sophisticated ones might have more costly, longer lasting materials and include decorative bumps in the metal panel, which give the finished product an aesthetically pleasing pattern of carvings rather than leaving an entirely smooth surface.
Lead and Gold were both particularly popular metals to use, primarily because both metals are relatively soft and can easily be shaped to make artistic patterns. The carved rock panel would commonly be made from a tougher stone like basalt, but on particularly sophisticated fusers would be made from obsidian with metal runes magically incorporated into the stone itself - a method of runecrafting that is far in excess of what is needed for these relatively simple devices.
Finally, in addition to flat-panel fusers, a variety of other shapes were also made. The most complex of these were column fusers, such as those used to finish the support structures in the various roads built between cities. These were made in several interlocking parts, allowing the fuser to be fitted around a column, encircling it completely while in operation, then removed after the process was completed. These were, naturally, made in several diameters, just as simpler single-piece devices were made to fit a variety of curves and angles.

Operation

In use, the metal panel would be placed against the stone to be fused and a magus that could read the runes would then simply recite key phrases from the inscription to activate it. Once activated, the rock it was in contact with would be heated to tremendous temperatures and the fuser would be magically pressed into the stone, creating enormous pressures within the rock being fused. The enchantment creating this pressure is also capable of providing necessary support to keep it from simply pushing a hole through the rock.
Over the next several hours, this caused the rock it was applied to to metamorphose. This was typically done with basalt, as the resulting stone was remarkably durable. However, several other source materials were used when basalt was not available, resulting in very durable structures, simply less durable than the fused basalt. Many of the ruined structures in Understone were produced using these inferior materials, once the city depleted its regular supply of basalt. This process also caused the surface of the rock to mold around the metal plate, allowing raised portions of the plate to be stamped into the stone.
Once this process completed, the magic would slowly deactivate, allowing the rock to cool. If a fuser was to be removed immediately, the rock that had just been treated would still be hot, glowing orange and fairly plastic. In more decorative construction, the fuser would be removed immediately, giving artists several hours to make smaller finishing touches to the design stamped into the rock. Otherwise, it would be left in place until the following day if possible for the safety of those working near enough to it that they might accidentally touch it.

Experimentation

In the years since the expedition to Understone was cut off from the surface, the gnome Hester Nopenstallen has spent some of their time trying the rock fuser they found on a number of materials, with some interesting results. The most interesting of these experiments involved testing it on a small amount of coal found in the ruined city. The process took an unusually long time, but resulted in the coal sample being pressed into a small diamond. It was riddled with flaws, making for a poor quality stone for jewellers. Further experimentation revealed that the resulting stone could be ground up to create diamond dust, one of the more expensive materials required for casting a number of magical spells.