I was recently comissioned to restore a Victorian fireplace. The white Carrera marble was layered in decades of paint and part of the left-hand finial was missing. My approach was to remove the paint using Bartoline TX10, one of the eco friendlier paint and varnish removers. I exposed the right-hand finial first down to the marble, enabling me to take an impression which would then create the cast for the missing part. I was persuaded to pay for a relatively new product -Siligum by Gideo- to make the mould. Rather expensive but well worth it, it comes in two parts which are squashed together. This rescued me from the dilemma of how to make a mould from a vertical object. When combined, you have around five minutes to push the material into place. After ten minutes you peel away the silicone impression and it's ready to take the casting material. While this was still in place and setting I continued with the rest of the paint removal -which fell in layers like curtains of garish colour reflecting changing tastes back through time. This excersise continued until the whole fireplace revealed the beauty of the original marble. Part archaeological, part forensic, every groove and valley in the mouldings had to be cleared to such an extent that I felt I was re-enacting the original carving process.
Gideo Resin Plaster was used to cast the mould as this is rock-hard and would come close to the marble in terms of durability. Once the mould had been cast the trick was to replicate the tones and lustre of real marble. Having made a flat test piece of plaster at the time of casting I used this to test colour on as it would reflect the nature of the mould. Paint is drawn very rapidly into plaster and it is important to wet it before applying any colour. This ensures a more even absorption into the material. This is actually a recreation of the 'secco' version of fresco painting technique where dry plaster is the base instead of fresh plaster. It was important to use very diluted paint. You could paint the plaster a similar colour as the marble, but you would lose the surface texture. The idea is to attempt to recreate the lustre, the transparency of marble. Actually impossible to do because it is in the nature of marble that light shines through it - it is translucent and plaster is not. However, with the help of some special paint (also expensive but worth it) I was able at least, to abtain something close to the sparkle of the stone. if you look closely at marble you see flecks of cristalline embedded into the surface. I was able to achieve this by using an acrylic paint by Golden called Iridescent Pearl. This contains Titanium Dioxide coated Mica particles which glisten in the same way. Mixed in with my other colours I managed to achieve that marbly, stony surface without which the cast would just look like painted plaster. Some grip-fix applied, and the finial was attached in place. When the client walked in and couldn't remember for a moment which side was being restored a warm sense of satisfaction welled up in me. Plaster into marble - alchemy. .. But that's another blog.