Fellow Shadow Watchers,
While recently making a reproduction of a 10"
octagonal Victorian??? dial (the client wishes to replace the flimsy
original with a more robust version in phosphor bronze) I've taken JPEGs
at various stages of the etching process. The first three show details
of a simple 'etching machine' I made some years ago to eliminate the
labour of dish rocking over periods of several hours.
There are many variables in the 'cloisonne depth' etching necessary for
sundials. For phosphor bronze hot fresh Ferric Chloride + agitation face
down in a dish will etch deeply in 2/3 hours.* Cold fresh Ferric
Chloride + agitation takes 7-9 hours. Old 'used' Ferric needs heat and
prolonged agitation although this can result in undercutting and
breakdown of the 'resist' film. There's no immediate substitute for
experienced 'know how' I'm afraid. I've been etching since the 1960s and
still encounter surprises.
*Etching 'face up' is slowed down or stopped by the slurry removed from
the metal settling back into the etched lines.
Etching 'face down' without agitation can suffer from trapped air bubbles
causing blind spots on the work. Plates MUST be supported above the base
of the dish by about 5mm to allow free flow of liquid and prevent damage
to the resist coating. I use small pieces of acrylic sheet with a slot
wide enough to slip onto the plate set 5mm from one edge.
The required strength is approximately 500grams of ferric chloride per
litre of water.
Supplies of chemicals and resists can be obtained from many electronics
hobby shops where it is used for making printed circuits.
SAFETY NOTES Ferric Chloride doesn't evolve fumes when etching BUT it
should not be left uncovered near metallic items which will be attacked
by vapour over time. It is an irritant so skin and eyes MUST be
protected and quite small amounts are potentially fatal if swallowed. The
exhausted fluid and the slurry it contains MUST NOT be disposed of by
normal drainage/sewerage or any method which will endanger, people,
animals, crops or water supplies. You should consult your local
regulations for its safe disposal.
If you are already on my sub-list to receive 'Making Metal Sundials'
JPEGs I will be sending these out in a few days time.
If you wish to be removed from the sub-list please let me know asap.
If you would like to be added to this distribution list let me know.
Best Wishes
Tony Moss
In response to popular demand I'm NOT including my gallumphing
auto-signature - for a while.
