We will try a variety of casting mediums to determine which one will best meet our needs.

The two items to be duplicated are an angel  approximately four inches wide, two and one half inches high and one inch thick; and a larger piece approx seven inches high, 16 inches long and two inches deep.

First I need to make something to reproduce the original item.  Since our  item has almost no "undercuts" and each part is (starting at the front) successively larger, the most common way of producing a negative for this item is to cast it in plaster.  Plaster is going to be the most easily obtained and least expensive way to create a negative mold of an item---from a prop to the human face.  It will give a relatively durable negative mold to cast with using a variety of materials including molten metals.  IF our item contains numerous undercuts or other characteristics that make it difficult or impossible to remove from a one piece plaster mold, then we may attempt to cast it in sections, and produce a multiple part mold for our project.

Other times you may need to cast your original item in a different material to create a mold.  You may need more detail than plaster  may provide (though this is doubtful in theatre quality work) or you may HAVE to use a more flexible material in order to remove the original from the mold (or the mold from the original)--This is a bit more difficult and time consuming.  We are going to examine one process that contains a few extra steps we will not use in our first project, but which will illustrate our process pretty well. 

In this process I may cast the original item in a more flexible medium--such as latex rubber, silicone gel, vulcanized rubber, moulouge  etc.  Since my first mould is "flexible" I can usually (sometime with a bit of work) pull the original item out of my mold without destroying it.  Even if I HAVE to make a small cut in my flexible mold, I can repair it with my casting medium.Using a RELEASE AGENT will help!  A release agent is something that coats the mold that your mediums will not stick to.  For plaster, I have used cooking oil, liquid soap, and silicon spray with good success. I might just cast now using this flexible mold---depending on the material I want to cast out of, the number of items I need, etc.  But suppose that I want to use something that would destroy such a soft and fragile as my mold is now made of---

There are several solutions:  One  way of doing this is the "lost wax" method---creating a SINGLE USE mold for the most part, though it can be adapted to create a multiple use mold in two or more sections.  We will not be using this process for this project, but may use it in a future project.  

In this process I may cast the original item in the more flexible medium--such as latex rubber, silicone gel, vulcanized rubber, moulouge  etc. 

Ok, NOW I have a flexible mold of my original!   Great---the problem is that it is FLEXIBLE and is going to rapidly deform--some mediums like moulouge will shrink rapidly in a period of hours, other mediums will stretch, and these mediums are NOT heat friendly, so casting in metal (for example) is impossible!  

So what I do is create another positive of the original in some other material that I can then destroy within a new mold. In the "lost wax" process, this material is wax.  I melt wax (paraffin) in a double boiler (some people use the microwave) and use it as my material to make a positive mould.  

Ok lets get practical, and use our example before you get completely confused!

Let us cast the angel head in latex, silicon, or some other "flexible" material. Let the mold dry, then pull the angle head out of the mould.  Now I have a nice flexible negative mold of the angel head.  However this mould will not let me cast very hot things in it (such as hot glue, and molten metals, etc) which I may wish to make my reproductions out of. In addition some of these materials may react with things like foams, or obviously if I have a latex mold it is going to be hard to cast my item in latex! To watch your mold melt or dissolve is not a happy time!

So we need to make a destructible positive.  We melt wax (CAREFUL if you get wax too hot it will BURN very well). Since we are using materials that might be heat sensitive, we will let the wax cool to just before it reverts to a solid.  If possible CHILL your original flexible mold while you are melting the wax.  Pour a SMALL amount of the wax into the mold and turn the mold in many directions---you want to move the wax around inside the mold to get a thin covering of ALL the inside of the mold.  Add more wax, again moving the mold around to move the wax throughout the flexible mold.  You want to add wax slowly--you do not want to stretch your mold, or overheat it, and you do not want to trap air inside. (More on air in a minute).  When you have filled the flexible mold with wax, let it dry completely. Now remove the wax positive mold, just like you did the original item you cast.

HOPEFULLY you now have a wax item that looks exactly like the original item you cast.  If not then we have to adjust the process.  The most likely problem you will encounter is that the wax mold is missing parts or has holes in it.  This is because you trapped air in the mold when you poured in the wax.  You might try recasting more slowly. tapping the mold to move air, etc.  If this does not work, then you are going to have to modify your mold.  WHERE is the air being trapped?  Put a SMALL hole in your mold at that place...that will let the air escape as you pour in the wax.  Some people have found that sticking one of those small coffee stirring straws though the mold where air has a habit of being trapped works very well.  These are vents to let the air out. It is OK if these tubes fill with wax as you pour--in fact then you KNOW no air is still there at that place in the mold.

Ok, you have solved all your problems---and have a very nice wax reproduction of your original item--- Now what?

Now you get to cast it again---but this time you can cast in a more sturdy and durable material.  Mix two parts plaster and one part water (see mixing plaster) to produce your material, pour it over the wax positive reproduction you made---you can pour pretty thick now to produce a strong mold---cover the entire wax positive EXCEPT leave TWO small holes for the wax to melt out of and other material to be poured into. One of these will be a air vent.  NOTE: some objects may require that you leave other air vents as well...you can create these by using those same "straws"....pour some plaster....lay in the straws, pour in more plaster, etc.

Let your mold dry completely.  

Now you get to destroy your wax positive.  Heat the plaster...careful you do not want to break it or make it "spall" that is flack off) until all the wax has melted out of the mold.  

Now for a single item, you simply refill the mold with some other casting material---fiber glass resin, melted lead, whatever.  When everything is good and set up (dry) you simply carefully break the plaster away---and ta da! you have your item cast.  

But you HAVE put in a fair amount of work for a single casting---which might (Murphy's Law) not come out as well as you would like---you have destroyed the mold....and now have to start all over---

THEREFORE:  I recommend a different approach.  

(1) After you have melted out the wax.....run your plaster mold through a band saw and produce two half molds!  This mold can be taped together, or wired together depending on what you will fill the mold with, and thus can be removed and reused---though you item will now have a small casting line.

(2) For more complex objects with lots of undercuts, etc--- When you create the plaster mold around your wax positive---create a multipart mold.  Cast a section of the wax, and let that plaster dry.  While it is drying you might stick a few holes into the surface of the mold....this will let you line up the next pieces later....some people prefer to put in a metal object such as a  couple of nails (put the head in the plaster you just poured).  After this plaster dries, apply a release agent to the dried plaster, then pour more plaster onto the old, continue the process in as many pieces as you need to complete the mold.  Now you can melt out the wax---but it is better to disassemble the mold and remove the wax item without melting it....this makes sure the mold will come apart and go back together again!

Now  put a release agent all over your parts and reassemble you mold---use the holes or nails to line up the parts-- and tape or wire the mold together.  Now you can pour whatever you want into the mold...and after it dries you can remove the mold in pieces to be reused later.  This gives you some insurance that you do not have to get the item perfect the first time---and also allows you to make multiple items from the same mold.

What materials can you make a casting out of?  Just about anything---depending on what you want the item to do....You could even cast in water (ice castings) and I have seen the wax replaced with water in the lost wax process---If you have a good freezer and don't mind some missing details--

For our purposes we want quick and cheap----those do not go together well!

We are going to try using several materials to determine which best meets our needs--in this part , we may screw up!  We are experimenting---

We are going to try to make our final objects out of:  Hot Glue, Caulk, Silicon Gel, White Glue and sawdust (wood and styro), and whatever we can find around the shop.  Once we determine which is going to work the best, then we will cast multiples in this medium.