What can I use to cast a mold from stone without hurting the stone?

Question

I'm new to this, but does anyone know what medium I would use to make a mold from a stone. In other words, There is an old building with a beautiful design sculpted in to it. I want to copy this design. I know there is a material out there that I can press against the original design and make a mold of it and then cast the design in plaster. I just don't know what material I would use to do this without hurting the stone.... Help!!!

Answer 1

I think the sculpey or any clay will work. If you use normal clay, any residue left will dissolve in the next rain, just don't use brown clay on light stone... if you use water based clay you would have to cast your plaster into the mold while the clay is still wet.
As the clay won't be very stable just on its own, you should consider making a mother mold on top of that. That is a hard shell, which just gives support to the soft part of your mold so it doesn't deform. It depends on the size of what you want to copy if you need it. You could make the mothermold from plaster bandages, but don't put plaster directly on the stone.
Before you start, consider carefully the shape of what you want to copy and where undercuts are and where you have to put in parting lines. What technique you use for mold making really depends on the exact shape of what you want to copy. If the structure is something complicated, you may want to practice how to make molds from more simple structures first so you are aware what causes problems and get some experience in how to solve them.

Another completely contact free method is if you happen to be at a university where they have a 3D laser scanning camera you can borrow, you could use the 3D laser scanner then make a model of your structure in the computer from the scans. That you could print out using a 3D printer. that way you can scale the model to any size (though anything large will be expensive to print)

Answer 2

This should be a two part mold.

First, cover the stone in Vaseline. Not goopy, just enough to ensure it slides right out of the mold.

Then, get a container taller than you stone.

Third, get some plaster (the kinds that set in 20-30 min are super easy) and mold one half of the rock.

Remove plaster and stone.

reapply Vaseline if necessary

Place stone in the other side up and pour the second half of the mold up to the other half of the stone.

You now have a 2 piece mold of your rock that will be good for multiple castings.

wash off your stone and it is good as new.

Answer 3

Actually, the Sculpey answer is a great one and does not require time to wait for plaster to set.

Really, any clay will work for this but Sculpey won't leave any noticeable residue behind. You just have to be careful not to disturb the clay between imprint and the setting of the plaster. Sculpey would be best because you can cure it without any significant change in size thereby making a permanent mold.

Most traditionally, you can use plaster to make the mold then cast with.

In any event you should get permission first. If they don't understand what you are doing and/or that it won't hurt the stone you may be setting yourself up for vandalism charges.

Answer 4

The simplest way I have found is to use Sculpy or Fimo clay. Roll it out into a sheet like pie crust and place it over the stone you'd like to mold. Press the sculpy evenly to pick up all the texture.
Then bake the Sculpy as directed (instructions on the box.) You can make a positive using the hardened sculpy mold.