Fibre Paper Re-use in Kiln Carving

“I would like to use 1/4 inch Fiberfrax to impart texture on the back of transparent glass.  Is there a way to make it reusable?  I tried mould hardener on a small piece of it, but the hardener wasn’t absorbed.  I’m afraid the fiberfrax will lose its structure if I pre-fire it (to burn out the binders) before removing it to apply hardener.”

 

It is difficult to reuse refractory fibre paper after moving it between firings, but not impossible.  I have used two processes. One is to place the glass over the cut fibre paper. This works for small pieces. The fibre paper was placed on thinfire to allow air migration out. I used a long low temperature bubble squeeze to ensure the binder was completely burned out.

The other arrangement I have used for larger pieces.  This is to assemble and fire the fibre paper to burn out binders.  There is a large chance that not enough air will get to the centre of the fibre paper when large glass is placed on top.  Binder not burned out leaves a brown mark on the fibre paper and stains the glass grey. Turn off the kiln once all the binder is burned out as evidenced by the paper returning to white.  As soon as the temperature in the kiln is comfortable, you can place glass on top of the fibre paper.  It is strong enough that it will not be compacted by the weight of the glass.

Using un-hardened fibre

But there is no logical reason for these processes, although they work. Firing to about 500ºC/930ºF with a suitably long soak will clear those gasses before the forming of the glass begins.  You will know when there no longer is a smell of burning paper, or on more recent fibres a chemical smell.  Make sure you vent the kiln during this burnout to allow the smoke to escape.  For a large area, a soak there may need to be hours long.  Another check is when the fibre has turned white again, the binders are gone.  A further protection against bubbles in any area is to place the whole assembly on a bed of fibre paper.

It is possible to use un-hardened refractory fibre without a separator, as the older versions do not stick to glass easily.  However, if you are using the current eco fibres, they will stick in many areas.  Kiln washing any fibre before firing is the best protection against lengthy clean ups.  It also allows the best chance to remove the un-rigidised fibre for re-use.

A smoother surface can be given to the refractory fibre, if you want. Do this by smoothing powdered kiln wash over the bed layer and any other layers the glass will be touching.  An alternative to powdered kiln wash is to put Thinfire or Papyros cut to shape over each layer.

After firing, slide the fibre onto cardboard or another flat stiff surface. Then place into a large pizza or similar box. I have stored fibre in such a way for several firings.

Using hardened fibre

Of course, the fibre can be hardened by use of colloidal silica.  Make up the whole stack of fibre paper for the kiln carving.  Harden the whole stack at once. This helps to bind the layers together.  Brush on the hardener to the exposed part of each layer.  Cover both horizontal and vertical surfaces. Hardener does take time to soak into the fibre paper.  Give it time.  You can add more hardener at intervals.  Be careful to avoid overdoing it.  Fully wet fibre is difficult to move and takes a long time to dry - days.  The objective is to harden the surface of the fibre, not to harden the whole by soaking it.

Allow the carrier of the hardener to evaporate for hours or a day.  When you can move the fibre, fire to at least mid-700’s ºC/ 1300ºF to 1400ºF.  After firing, it must be covered with significant amounts of kiln wash. This can be as a liquid or as powder. I prefer liquid.  The kiln wash is required over all edges and surfaces to keep the glass from sticking to the fibre.

Storage of the rigidised fibre paper can be in the same way as for the fibre without binders or hardener.