Hard Gold Plating allows gold thicknesses up to 5 microns
(M10-6).
Known as "Hard" because
there is a small amount of alloying which reduces it from 24ct ie pure to 23.9ct. This addition doubles the hardness
of the deposit.
Deposits are generally
porous up to 2.5 microns and so if plating directly on to a tarnishable substrate 3 microns (average) is recommended
in order to prevent tarnishing of the substrate metal through the gold.
An intermediate layer of
Bright Nickel is often used to protect the substrate metal from corroding and due to the nickel's hardness the sandwiching
effect allows greater longevity of the gold top layer.
For gold deposits worn
(jewellery) or regularly contacted (contacts, grab handles) we recommend a minimum deposit thickness of 1 micron
per year.
Pure Gold Plating allows gold thicknesses up to several millimetres (mm).
Pure Gold Plating is used
for industrial applications where either high purity of deposit is required and/or greater than 5 microns deposit needed.
Pure gold is often used in place of Fire Gilding (mercurial gilding) which is no longer allowed in the EU due to the
very high toxicity of the process. The colour of the deposit being pure is identical to original Fire Gilding and can be burnished
in a similar manner.
