The heating process of the stones is performed using an alumina (99.96% purity) muffle tube, COE (Close-One-End), OD=80 mm, L=280mm mm, fastened hermetically and securely with metal flange assembly.

In this mode, selected gases generated in the atmosphere control module can be purged directly to the muffle in "open-loop" mode, thus providing controllable atmosphere conditions with positive pressure up to maximum 1800oC temperature, or in vacuum -up to maximum 1500oC. The crucible is loaded in the chambers from the bottom using mechanical elevator and supported by special reticulated alumina post.

SELECTIVE LOADING. The unique feature of the M80N-1700 is the ability to load small quantities of ruby-sapphire in 6 alumina (99.6% purity) dishes which are inserted into the crucible and then in the muffle. Each dish is OD=59 mm, H=16 mm (each dish 321 cts, total 1,926 cts); the 6 dishes fit into one crucible OD=70mm H=100 mm. In this mode, stones from different localities, or stones with different features may be grouped and heated together on the same time, under the exact heating parameters without been mixed or contaminated each other. Likewise, fluxed and unfluxed stones may be placed in different dishes. Loading these stones in this method is particularly useful in research heating projects where contamination must be avoided and precision is required.

BATCH LOADING. To obtain maxiumm load capacity (3,380 cts) the corundum may be loaded in one crucible and inserted into the ceramic muffle tube. This mode is suitable for heating corundum in the bulk with or without using additives.