Abstract: A single furnace loading cycle technique and a ventable sintering box therefor are disclosed for the sintering of products, such as, ceramic substrates. The sintering box includes a closeable cover which is held open by collapsible or deformable or sensitive spacers in a first furnace temperature range. The sensitive spacers collapse or deform in a higher temperature range to seal closed the box and the substrates therein. Additional spacers may be used for applying weight upon the substrates at the higher temperature range. Thus, volatile agents within the substrates are permitted to escape in the first temperature range but are prevented from escaping in the higher temperature range and in situ sintering weights can be applied without removing the substrates from the furnace.