I've just finished an experiment making a replica of a part of the hoard's surface. We want to have a replica of the hoard "block" as excavated because the conservation treatment will of course turn this into 70,000 seperate coins, probably spending most of their lives in tupperware boxes in a store. To have a permanent record of it in one piece we decided therefore to laser scan the entire surface so a to have a virtal 3D replica but also to make a more old fashioned physical cast. In order to do this I painted a liquid silicone rubber onto a part of the surface and let this harden after a couple of hours. I then applied a second coat of rubber, this time thicked to a consistency like Icing. Once this too had gone hard after twenty four hours I was able to peel this mould off the surface of the hoard. This was the important bit as it was a test to see if the rubber would damage the surface and pull off coins. In the end only one coin came loose and it may actually have been loose before. The coin was carefully laid back in place for later recording.
I now had silicone rubber mould of about 15 x 20cm with which to make the copy. I did this by painting a thin epoxy resin onto the mould's surface. Once this had set I applied a second layer again thickened almost to a paste. Once this set I peeled off the rubber to reveal the new resin copy. The detail was very good but the resin was of course uncoloured. I therefore painted the surface with a variety of enamel paints to copy the various browns and greens. The whole excercise worked well and means that quite soon I'll go ahead and do the whole hoard. It's so big that I will have to cast it in sections and join them later but this shouldn't be a problem. What is a problem however is the very fragile gold jewellery. The thin crumpled gold sheet would be dragged right out from the hoard with the rubber if I tried to mould it so I shall have to leave these areas alone. Plan B is to have these sections laser scanned and resin 3D prints made from the results. I will then make epoxy casts of these areas from their prints and incorporate them into the whole replica structure. I will probably gold leaf the jewllery in the replica to get a good finish.