This work also requires frequent annealing, for otherwise the wires or tubes would rupture.
Further, all the subsequent processes of cutting, moulding and annealing become increasingly difficult, owing to the greatly increased risk of breakage arising from either external injury or internal strain, as the dimensions of the individual piece of glass increase.
The second system is especially used for annealing large and heavy objects.
Types of muffle furnaces are figured in the article Annealing, Hardening And Tempering.
The heat passes from the melting furnace into the annealing kiln.