Thread: Woodburning Fading - An attempt to understand .

Originally Posted by Mike the knife

Here are my experiences with wood burning , interpret them as you will, I too find it counter intuitive that carbon (burnt wood) can fade & relatively quickly too. Yet there are charcoal drawings from the renaissance surviving! Those prehistoric caves in France have pictures draw with burned stick ends & other pigments that are dated to 32,000 C ! Still they haven't been exposed to the sun.

I had a birch plywood tray with deep wood burning on it from Romania , it had a VERY thick coat of varnish on it, it lay around for 30 years in poor light - it did not fade.

My father burned his house number into a piece of wood crudely a poker heated in the fire , it was easily 1/4" deep then he dipped it in marine varnish ( with UV. filter) it was very thick indeed! No sanding , brushing or rubbing all the charred wood was left intact. This was screwed to the gate in the full sun , within in 5 years you couldn't red the number, the varnish was relatively sound !

20 odd years ago I used to sell pyrographed clocks burning into sycamore, they were very finely drawn & included both deep lines & light shading which involved lightly searing the surface of the wood for subtle shading, they were then given a thin coat of acrylic varnish. A clock that I had on my mantle-piece in a well sun lit room ( but not direct sun) faded, the very light shading completely vanished without trace within a year ! Less strong lines showed signs of serious fading after 5 years , the deeply burned lines survive to this day but are much more brown than the original fresh black.

A wall clock hung in a dark corner of a dingy dark room has fared the best but the lightest shading burning has disappeared.

As soon as I noticed this fading I investigated varnishes with UV. filters but was told by all four of the the major manufacturers that 3 thick coats (of an already very thick varnish ) minimum was required to offer even a maximum of 20% filtering in ideal conditions .I stopped making clocks as they were upmarket & expensive, I don't want to let anybody down.

Of course we are not talking about pure charcoal which is always made in oxygenless conditions & out of certain wood species . have look at this http://www.vias.org/church_paintchem...paint_107.html maybe our pure carbon isn't so pure ? It looks highly likely the fading is a result in fact of chemical instability.So given that the carbon resulting from pyrography is an impure mixture of various wood tars ,oxidized materials & carbon which will be highly acidic , corrosive & have a strong destabilizing effect on the pure black carbon pigment . Add that to the undoubted fading affects of sunlight , ie. destabilized pigment soup + the bleaching effect of the sun = that I fear there is no practical way to make the burnt marks stable & permanent !

Since writing the above I've had the chance to talk to a research chemist I know socially who commented - " Yes that seems entirely plausible " - which was a relief for an unqualified arty type guy lie me sticking my neck out ! Not good news for number of folk here though- sorry but it is probably best to know than not know.