What is the "Wax to Metal" Shrinkage?

 In honour of  our own "Taf Schaefer, on Ganoksin", who asked me one simple question. "Gerry, What is the percentage of shrinkage when you're casting metals?

 Our own "Taf" mentioned to me that she does a lot glass designing with the "Steuben Glass Company". In fact, she was one of the leaders with that fantastic glass company where I once visited in Upper area of New York State, USA. You can see some of her wonderful sculpturing at "Stueben.com" and to think she is one of 'us' on Ganoksin. We are all honoured, as I am for sure, just go to their website and see many of her beautiful designs. 

 My answer was given to her, in the following email, shortly after I heard of her question, it was a simple 0.6%. But here comes another question.  How do the jewellers arrive with that answer?

 There is some background to this question, if I didn't remember the answer, I went directly to the Google for the basic information, then I'd search further. Here is another answer for her and everyone to use.

There is some history to this question;

 In 1800's, the jewellers in those earlier days used gravity to get the molten wax to into their own metal molds. Thankfully, we don't now use that "gravitational process" anymore to get our wax into those rubber molds.

 First of all, the wax is under pressure and forced into a rubber-mold. The pressure is about 25 P.S.I. (Per Square Inch) and that is sufficient enough to get the molten wax into all of the cavities of the rubber-mold. 

The next query got answered, how do you get the wax removed from the two halves of the rubber mold, without getting the wax broken or destroyed in the removal-process?

 Google mentioned using a basic "Lubricant" that is in having "Talcum-Powder" as a the guide. I knew this for myself after seeing this first-hand, when I was learning my Diamond Setting, some 63 years ago. I took so much for granted then, but not understanding the real reasons. If that jeweller said 6%, I took it for granted that he/she were right. But never ever, questioned them...!!!

 Today, we use a liquid to spray the rubber-mold to extract the warm wax from the rubber. When we get the wax removed WE MUST GET ALL OF THIS WAX CLEAN from any powder.

Some jewellers immerse the 'powder encased wax' into a water-based solution. Why is this so essential? This will give you a spotless clean wax, that is free of any powder, or other substance.   

 When the "weighing process" is initiated, this wax form MUST BE TOTALLY CLEAN of any extra powder-like materials. Not to mention, that every wax pattern MUST be clean of any 'extra' wax residue, this will give you "any not wanted wax" and will also give you any of that metal in your final weights. Your wax should be visually clean!!!

 If I'm repeating myself, that is because this step is so darned important, in this "weighing process".

 You can use any method, just to get any 'remaining wax' totally removed. I use any file of shape, grit and texture. I even bought some of these above shown files from my favourite "Dollar-Store" outlet.

At times, I will use my graver and hand-remove any of the remaining wax, as shown below.

 If you can see a little 'extra' wax, try and remove everything. Those few 0.01 - 0.02 grams can add up to unnecessary $$ out of your pocket.

The "RATIO of 0.6%" is now being started, but how is it found & using what method? 

Let's first state that we use this ratio of  "WEIGHT X HEIGHT X DEPTH". This will easily give you the VOLUME. But what about the 6% and how is that arrived???

Taf Schaefer then asked me for the second question, will a "thick wax-sprue give us any problems", my own answer will be a definite "NO"! If you need any thick sprue, attach that AFTER the "6%" answer has been calculated.

 Now just compare these two measurements, "with & without" that center sprue.  This will be an interesting weight difference, agree? 

The difference (in grams) is enough to give you a totally wrong weight answer. There is a great difference of 0.26 grams, if you multiply those numbers in gold. Good grief, those are dollars flying out of your pocket. Do you really want that to happen?

 BTW, "Taf Schaefer" with everyone, this my answer for you. You can attach those thick sprues after your final $$$ numbers are easily calculated. 

How is that 6% calculated, this is a very detailed answer and so easy to understand!!

Original Metal form to your machine (squeezed) hot rubber created mold there will give you a 2.5 % shrinkage. A "Cold Mold" will not give you any of those shrinking problems.

 BTW, this is a metal model is of a "Ballerina", she was created in England in 1934. This prized model now sits in our home as it was passed down from my "Beloved Parents" ever since.

 You can see just how that there is NO SHRINKAGE HAS TAKEN PLACE.  This cold mold refers to the fact there is no squeezing of any two hot plates for the top and the bottom. This method literally squeezes the two very hot plates and makes the rubber also very hot. Every few minutes, the two plates are squeezed again, each time closer together. At every squeezing action the temperatures are quickly measured...Squeezing again, another temperature check. few more squeezing's, until all of the hot-plates are finally FORCED together.

 Just imagine how much force is being brought together? Now think of the shrinkage percentages, good grief. I couldn't even suggest a simple 2.5%, but that is how those numbers are being created.

 It's so hot, that all of the semi-liquid rubber is forced into all of the crevices and recesses of a cluster ring with it's all kinds of detailing's. As for this "Ballerina" model, such a process is not needed, hence a Cold Mold will easily suffice. Plus there is no hot squeezing is needed or required. NICE?

This shrinkage problem that we're talking about is at a absolute zero...WOW & finally!!! 

 To calculate the difference of answers, I suggest that you use the "trial and error" method.  Comparing one method against the other, you will be pleasantly $$$'s surprised.

ANY wax will shrink from the Rubber mold at 1.0 %

Casting metal from the (Wax) Rubber Mold is at 1.0 %

Cleaning (filing) & Polishing (using the Tripoli & Rouge compounds) is another 1.0 % +.