Which grades of gold leaf remain durable outside the building also without a protective coating?
In the open air, only the gold leaf grades above can survive without a protective coating 23 carats. that means, that all grades of gold leaf below 23 carats contain so much copper and silver, that the corrosion of these components would cause stains on the gold layer.
Please explain the specific features of transfer gold.
Transfer gold is gold flakes pressed onto tissue paper. Therefore, they can be cut with scissors and applied even in stronger winds. However, this type of gold leaf is only suitable for oil gilding. With pulment gilding or behind glass - with the use of gelatin – the tissue paper would also be wetted, which could not be removed from gold leaf.
What metal foils must have a varnish layer to protect against corrosion?
Silver leaf and stitch (so-called. schlagmetal) corrode and therefore need to be protected with varnish. Outside the building, also gold leaf having less than 23 carats must be varnished.