Fornace per la calce

The alpine economy of self-sufficiency and self-production has determined that even the houses in the mountains were built using exclusively local materials: wood and stone.

Local stones were used for both the masonry and the roof (lose), with lean lime used as a binder that the builders had to be able to prepare.

Within the park, in some well-defined but distant areas (also sharing the same place names, namely laz Oure), a series of ovens called "calcare" are visible, where sedimentary rocks consisting primarily of calcium carbonate (calcite) were transformed into "quicklime." They bear witness to a once completely forgotten productive activity.

In the Susa Valley, the abundant availability of limestone rocks favored such productions, with evident differences in processing between the Lower and Upper Valley: while in the Lower Valley the kilns consisted of stone constructions shaped like truncated cones with specific combustion chambers, in the Upper Valley lime was prepared using a faster method similar to that for charcoal production.

A pit was dug or an existing cavity in the ground with a diameter of 2-3 m was utilized, with its walls finished with a dry stone wall.

A large amount of wood was stacked inside and a dome was built using lime stones, using smaller fragments to fill the gaps above. A hole was always left at the top and it was covered with grassy bark, and the wood was lit through an opening, which later served to provide oxygen for combustion.
This process, being tied to the non-renewable amount of fuel, produced lime in smaller quantities and of lower quality.

Each production cycle involved a series of quite laborious operations and the firing lasted from five to six days, during which the lime kiln was kept continuously lit.
To feed the slow and continuous fire, a large amount of wood, especially in bundles, was needed. Loading also took quite a long time because the stones had to be split and arranged above the fire bed.

After the firing was completed, it was necessary to wait for the kiln to turn off and cool down before extracting the resulting quicklime. This was a "quicklime" which, to be used, had to be slaked first by adding water, causing a lively exothermic reaction transforming it into "slaked lime."