Metal leaf and the problem of oxidation
Let’s get one thing straight right away: metal leaf oxidises, however it is processed. You can slow down the oxidation process or even intensify it – whether intentionally or unintentionally – when processing metal leaf.
We have put together a few facts regarding the subject of metal leaf.
- Workshops/building sites – The humidity level of the workshop of the building site must be controlled. A humidity that is too high will speed up oxidation when processing metal leaf. The ideal workshop or building site features air conditioning in summer and heating in winter.
- Substrates – The substrate that is being treated with metal leaf should be clean, free from grease, sealed, varnished, and outgassed. Tip: as long as the varnish is still outgassing and smells, it should not be gilded with metal leaf. Freshly varnished surfaces constitute a high oxidation risk for the metal leaf/copper.
- Adhesives – Strictly speaking, there is no adhesive that is suitable for metal leaf, as these always promote oxidation of the metal. The chosen adhesive must be applied thinly and allowed to dry fully before further processing.
Processing and methods
Metal leaf should always be stored in a cool, dry place, and should always be keep well sealed in a cardboard box or booklet. It should also never be touched with the fingers, as fingerprints continue to oxidise even under a coat of varnish. You should therefore always wear cotton gloves when working with metal leaf. Caution: In summer, hands sweat and gloves can become moist. They may not be particularly comfortable, but the best solution is to wear latex gloves under your cotton gloves.
- Varnish coat – Metal leaf must immediately (always on the same day) be protected from oxidation with a varnish coat. Tests are always essential, as varnish manufacturers are constantly “optimising” their varnish formulae. This varnish optimisation can often lead to unexpected problems with surfaces gilded with metal leaf. In the case of large surfaces, a second coat of varnish should always be applied. Accidentally missing a spot when varnishing quickly leads to oxidation and costly complaints.
- Brush/gun – When overvarnishing, always use clean brushes. Thin coats of varnish are essential. When using a paint gun, the first coat of paint should always be sprayed thinly. Always operate compressed air systems with a refrigeration dryer. Moisture in a compressed air system promotes oxidation.
- Restoration – Even well-gilded and varnished metal leaf will slowly discolour over time. This makes restoration difficult, as a partial new gilding procedure must be tinted with great effort. Usually, a completely new gilding procedure is the fastest and therefore the most cost-effective solution.
The cost factor
The item to be gilded, the financial budget, and a long-term cost comparison are the criteria for deciding upon a material.
Gold leaf or metal leaf? An easy calculation
In the case of oil gilding with gold leaf, material costs can be 2-3 times as high as labour costs. The labour costs incurred for oil gilding are comparable to the use of leaf metal. The additional costs of working with small leaf gold sheets are offset by the redundancy of overvarnish, which is necessary when working with a leaf metal surface.
Material costs for metal leaf/copper leaf compared to gold leaf – a ratio of approximately 1:40
A short example
€1,000 gold leaf + €2,000 labour costs = approx. €3,000.00
€25.00 leaf metal + € 2,000 labour costs = approx. € 2,025.00
The first gilding with metal leaf is always cheaper. But by the time of the first restoration of the metal leaf surface, it becomes expensive. The total costs for metal leaf gilding + first restoration can exceed a well-preserved gold leaf surface by up to 35%.
Example of total costs after 1 restoration
€50 metal leaf + €4,000 labour costs = total cost of approx. €4,050.00
The gold leaf surface (from 22 carat interior) must not be overvarnished. This saves both materials and a lot of time. The gold leaf will not oxidise and will retain its metallic surface with a natural reflectiveness and eternal shine.
Metal leaf is a reasonably priced material for short-term surface metallisation, but, in the end, annoyance regarding oxidation will outlast the joy caused by the lower initial cost.