Creating samples or tests provides both references on firing
profiles and knowledge of the characteristics of the kiln.
General samples
Sample tiles are normally a series of tiles with the same
lay up but fired at different temperatures.
These are likely to be intervals of temperature from a sharp tack to a
full fuse. A suitable interval might be
10°C as it is easy to interpolate between these for a slightly different
profile than the tiles show. This is the basic arrangement.
You can make this more informative by including tiles in the
same basic lay up but with hot and cool colours, opalescent and transparent,
black and white, strikers, etc. The
addition of these will give a richer bank of information.
Of course, these tiles must be labelled with glass types and
code numbers and the temperature used.
This is not all the information required though.
Many sample tile sets do not include the firing rate. The heat work required to attain a specific
profile is dependent on time, temperature and hold. These are the time to get to the working
temperature, the temperature, and the soak time. If you do not record the ramp rate used, you
will have incomplete information. It is
not that you have to record the entire schedule. But the rates and any soaks on the way to the
top temperature need to be recorded. This means you can take account of any
slower rate of heating, any additional holds on the way up, and the length of
the soak at top temperature. Then when
contemplating something more complicated than the conditions under which the
tiles were made you have better information.
It is a good idea to maintain a photographic record of the
sample tiles to avoid storage problems.
These can be made from the individual tiles and photographed from
several angles.
Another way of keeping records - without making tiles for
each temperature - is to photograph the tiles through peep holes as the set
temperatures are achieved. This means
the tiles need to be placed in the kiln so they can be seen from the peep hole.
You will only have a physical sample for the top temperature. The other
profiles will have a photographic record.
The firing conditions for these need to be recorded just as for the
series of physical tiles.
This photographic record may not be suitable for your way of
working and so require making the sets of multiple tiles. Both these methods provide a generalised
record of heat work to achieve given profiles.
Note that you will need to prepare sample tiles for each kiln, as each
has different characteristics.
Specific samples
However, there will be cases where the general conditions
exemplified by the reference tiles are to be exceeded.
In this case you will need to make a sample specific to the piece you
are planning. This can be a general
representation of the piece, or a scaled mock-up.
The general test tile may be small scale or relatively large.
It will contain only the components in
terms of height and shape that will be in the planned, but more complicated
piece.
A more rigorous method is to make a full scale – or nearly
so – mock-up of the piece. This is usually done in clear. Fire it to the
proposed schedule to determine the exact effect.
Sample making gives confidence in preparing work for the
kiln and scheduling to get the desired profile.
