Simultaneous Firing of Different Moulds

Often you have moulds of different sizes or depths that you would like to fire at the same time to use the space or save time.  If the moulds are of distinctly different sizes or shapes, you will not save time, as the likely outcome is that some will be over-done and un-shapely or, conversely, that some will not have completed their slump.

The main things that act against firing moulds with distinctly different firing requirements are:

·        Moulds with different spans require different temperatures or different soak lengths.

·       Moulds of different depths, even if they have the same span, require different soak lengths.  

·        Moulds of different shapes, even if they are the same depth, require different soaks or different temperatures. 

As an example, if you have two moulds that require less time or lower temperature than three smaller ones. If you get the smaller, relatively deeper ones fully slumped, the larger, shallower ones will be more marked by the mould than necessary.

The best thing you can do if you want to make full use of the kiln space each time you fire, is to save up the glass until you have enough to put in a full kiln load.  This may require more moulds of the same size than you currently have.

Usually trying to fit in a lot of slumping into one firing relates to a concern on how much electricity will be used in multiple firings. However, the kiln does not use huge amounts of electricity.  A 50cm square kiln will normally use less than 10Kwh for a slump with a long soak.  This will cost much less than a glass of beer or wine.