credit: Scarva
Material
Rigidisers are colloidal solutions of silica or quartz with
a carrier of some form. It is
also available as a powder to mix with water according to the instructions.
Health and Safety
Silica and quartz (sometimes referred to as flint) in dry
powdered form are a serious health risk.
Wear good respiratory protection and long sleeves and gloves against its skin irritant. Work outside with
the powdered form to keep the dust out of the studio. Clean clothing
immediately after working with the powdered form of rigidiser. Wearing gloves is a good idea whenever
working with rigidisers, as the wet form is also a strong skin irritant.
Application
Mix up the powdered form as 1 part powder to 4 parts water, by volume. Do this masked and gloved, and outdoors if possible. If not, have a HEPA vacuum running next to your work area. Mix thoroughly and allow to slake for 24 hours. Then mix very well by hand or with a blender. Strain the mix to remove any clumps - they can be made into a paste and added to the main solution.
Liberally paint the solution onto the refractory fibre. Stir prior to use and frequently throughout the application to keep the silica/quartz in suspension. Depending on permanence, coat one or both sides of the paper/blanket/board. It is not necessary to soak the fibre completely. The object is to provide a hard surface. It does not need to be hard throughout.
Flat Board
It is best to apply rigidiser on both sides of refractory board. If rigidising both
sides, allow one side to air dry before turning over to coat the other side. By coating both sides, the warping from heating
on one side is reduced.
Slumping forms
Cover the shape you are taking the mould from with an
impervious separator such as Vaseline or thin plastic film. Prepare the fibre blanket by coating both sides of
the fibre with the rigidiser. It does
not need to be completely soaked. Press
the fibre firmly into/onto the shape and especially into any depressions and
around any protrusions to be certain of a faithful replication.
Curing
Allow the refractory fibre to air dry. Or if needed quickly, you can kiln dry at 90˚C
– 110˚C / 194˚F – 258˚F for several hours. But only if the master mould can withstand the
heat. If not, demould only after the
fibre is dry and can hold its shape without the master. Be sure to remove the master mould from the fibre before
proceeding to heat cure.
When air dried, cure in the kiln by firing to 790˚C/1454˚F
for 20 minutes. Before firing, place the dry form on a
refractory fibre separator to avoid the silica/quartz sticking to the shelf. A
rapid rate straight to the top temperature is acceptable. After the soak, turn the kiln off, as the rigidised refractory material
is not subject to thermal shock.
In Use
Coat the hardened fibre in kiln wash, or cover with shelf paper or refractory fibre paper, to avoid glass sticking to the hardened board. The bare surface of the rigidised form is now coated in glass fibres and they will stick to the glass unless a separator is applied.
When used as a shelf, it is best to turn the board over after
a few dozen firings. This helps counteract the warping tendency that rigidised
boards have.
