Thread: Label casting failure

I agree wiht DJ .. it's a void. The dreaded 'silvery shimmer'.

It is an air pocket that can develop at most any time. I've had some great looking castings
develop these after being finished!

There's a few things that can cause it (at least, that's my understanding .. could be many)
but one of the more common causes (in my limited experience) is that the resin is set,
but not quite cured. If it is still flexible at all, you can 'twist' it while turning, you can warp
it while removing form the mold, you can overheat it while sanding .. anything that will
change the size, shape, dimension or the blank OR THE TUBE can cause this.

When you move one but not the other (tube or blank) then an air space can be created..
and that will give you the shimmer. If you heat up the blank while sanding, it can cause
parts of the blank to expand away from the tube. (shimmer) or if you get a small 'catch'
while turning, it can cause the blank to move while the tube stays put (shimmer) or
if you need to push the blank out of the mold with any force at all, it can cause a
slight separation of the blanks from the tube (again.. shimmer)

My advice in that case would be to pour the blanks and then set them aside for a
few days before turning them.. and gently remove them from the mold. turn with VERY
sharp tools and watch for heat.. wet sand only, and stop when they start to get even
a little bit warm. In fact, you could remove them from the mandrel and put them in some
cold water to col them off.

WATCH OUT for your mandrel and bushings.. they can retain A LOT of heat when
sanding!! Might not hurt to keep a large can or jar of water close to the lathe .. and then
just dunk the whole thing in cold water .. mandrel, bushings and all.


Another thing that can cause the shimmer is air leeching out from the label material
itself. This is why some turners use a sealer coat of some type on the labels. It will
depend on the label material, of course, but some are more apt to trap air than others.
And then the resin gets warm, the air bubbles come out of the paper label and they
expand (shimmer!) Some casters also 'paint' the labels with resin before they pour,
it seeps into the labels and can displace some or all of the air inside the label.

There are so many variables .. temp, humidity, mold materials, horoscope etc. that
it isn't feasible to come up with one cause for this problem.. and that's even before you
get to the variables of the resin and labels themselves.

But don't feel too bad, you're not alone. I know 'professional' casters who have been
doing this for years and years ... and once in a while they still get the shimmer.
The best you can do is make yourself a checklist (yes, write it down and check it off!)
to eliminate all the variables you can.

Warm the resin, warm the molds, degas the resin if possible, seal the labels, vibrate
the mold after pouring, pick out all the bubbles you can ..

.. and then leave the casting alone for a few days.

It will still be there.. I promise.