newbie asking for help

[do99ie]

Hi and thank you for allowing me to join your group. Can anyone help me please. I am UK based and a keen metal detectorist. I recently found a rather nice Roman brooch. Unfortunately I will not be allowed to keep this and it will have to be handed to the museum, I have at the moment, got possession of the artefact but noises are being made for it to be deposited into the waiting arms of the museum. I have tried to make a replica using sculpty both as a "negative" moulding and positive cast. Not a great deal of success. I've used a sand system of casting from the positive cast, not a bad result but not that happy with it and have been researching silicone reproduction casting. Then will try a lost wax method. I should say that I'm using pewter at the moment but eventually hope to cast one in silver. I have purchased a small quantity of rtv and need some advise as to release agent. I need to be able to cast/replicated the brooch without causing any damage or leaving any residue on the surface. Any help would be greatly appreciated Regards Rod

 

[Propsjonnyb]

You'll need to buy a high temperature RTV silicone for casting hot metal (pewter) and especially silver, ordinary talcum powder can be used but you really need some graphite dust to do it properly , you'll also need a furnace pot and a thermo-probe. ( as well as the associated protective gear - gloves , goggles, casting apron , etc ) To start -first build a box for your item , four sided - I make mine out of thin plywood and duct tape them together ( you want to be able to use it again ) use a piece of blue tack and fix your item to the bottom of the box , don't make the box too big either , you don't want to waste that expensive silicon, calculate the volume of the box , just going - say a half inch higher than the item surface, this is the volume of compound needed , mix it according to the makers instructions and then slowly and carefully pour it into the box ensuring you cover all the item . Now let it set - overnight at least , now you de- mold, carefully remove the box remove the blu-tack and using the talc and a fine brush as you peel back the silicon, dust the inside liberally with the talc , once you get past a certain point the item should pop out quite easily. Now draw a bowl of warm soapy water and wash both the item and the mold , use an old tooth brush , when clean - dry them off and put them both in the airing cupboard . Now you have your mold dust it with a very soft brush using the graphite powder , do not try to crush up pencil leads , it is not the same thing !! , ( a make-up brush is ideal) wear a dust mask while you do this - your lungs will thank you later !! Build the box back around the mold and then dust the mold and the box all over with the graphite. Turn the box over and tap out the excess dust. Your mold is now ready for casting .

I will only take you this far, as your post clearly shows you have no knowledge of hot metal or lost wax casting .

I would suggest you try casting the part in resin first a few times before you try hot metal, as it is not for the untrained hobbyist and if this is your first attempt, as I suspect it is , do not try this at home!! , go and take a course at your local polytechnic or art school first !! , as I will not teach you on an open forum , hot metal casting is NOT for the beginner, it is highly dangerous and you can get seriously hurt or kill yourself, if things go even slightly wrong ! pouring hot metal into the wrong type of silicon mold - the metal will cut through the rubber like a hot knife through butter! or boiling water on an ice cube !! if you're not suited up you could get seriously burnt, or worse

You may find adding metal powders to the resin - as some do here- a much better alternative - as it will polish up and look identical to a cast metal piece without all the hassle .

 

[Jabberwocky]

The curiosity is killing me! Could i see some pics of the brooch???

I'm a sucker for roman history

 

[Keiko]

I don't understand - why must you hand it to a museum? Is there some such law in the UK? Are you being compensated for this?