Delft Clay, Sand Casting

I want to brag share this with you. Here is my 13 year old baby's last year's school photo project. The project required him to make hand made medieval artifact. Not thinking very long, he decided to use the materials he had at hand, and he had 3 oz of pure silver and a Delft Clay Sand Casting set. What else could be found in (at the time) a small jewelry workshop?

On the project he got an A+.
At first he made a model of his personal coin, with his proud face and inscription on the back, and his favorite symbol on the other side. Some delft clay was prepared and everything readied for the casting.

 


A blowtorch was readied, and an awesome face was practiced before-hand. :)


 


And this is my favorite photo. I love to photograph melting metal . :)


 


The casting went successively, and the coin was cleaned from bits of burned clay. By the way, I do not suggest preforming a delft clay casting without some good ventilation. Do you remember the smell that always accompanies trains? Well the same smell of burning oil, earth, and coal will be absorbed by the walls. And after a few castings without good ventilation, the room would probably smell like a train depot.


 


 The excess metal is removed.


 


And now the most annoying and consuming part : the finishing of the coin. When it comes to wasting metal, and time, Delft Clay, or Sand Casting, takes the cake, (except for maybe sculpting something out of a piece of silver).


 


My Son chose a very difficult model for casting, because it was two sided,  it was very hard to cast it without damaging the coin. Before attempting tho make the coin, he first planned out where the air vents, and the metal funnel was going to be located. The weight is 79 grams of pure silver. He did the entire project all on his own, and I only helped take photos, and poured the silver into the mold, because holding the torch, and pouring the metal at the same time, is quite hard.


And now my "baby" is professionally melting metal, knows the different stages of readiness of silver, can tell apart pure silver and un-pure silver by it's behavior during the melting. I'm so proud! :) 

Silver Refining. Part 3

The participants of the third part are: a power source (in our case this wonderful pro-plater, basically an ordinary powerful power source), half of a 2L pop bottle, a tea filter (a coffee filter will also work, but as tea filter is more comfortable to use), a stainless steel fork, some insulating tape, a brass rod, and a thermo-shrink pipe (Its missing on the photo, but will soon appear :) ). The hero of last time's epic tale, the silver ingot, is gone, but instead, we replaced it with a silver blob. We thought it would be a more comfortable fit for a not-so-deep container.

 

We take a strip of pure silver, and weld it to the blob . We bend the end of the strip for better hangability.

 

Now we make two wonders of modern innovation. A cathode electrode made using the help of a fork, insulation tape, and some pliers and an anode stick, made by putting the thermo-shrink pipe on the brass rod. The pipes are cut, keeping in mind the distance in the center, and to the side, the center being where the blob is going to hang, and the end is where an alligator clip is going to be attached.


 


 This is how the complete piece looks. An electrolytic bath, in the pop bottle variant :) .
Attach the tea filter to the anode stick and hang the blob in the middle, and then check the conductivity between the rod and the blob.


 


This chemical jar contains the very first dose of silver nitrate, form the first part (32 gram of silver/80 grams of diluted nitric acid). We dilute the mixture with distilled water till we have 1L.


 


We submerge the cathode-fork into the electrolytic bath, and pour the silver nitrate in. We make sure that the silver nitrate doesn't touch the joint between the strip and the blob. The worst case scenario, the joint gets diluted, the blob falls down, and the reaction stops.


 


 We attach the minus electrode to the fork, the plus to the brass rod, and turn on the electricity. In the process we make sure that the voltage is between 4-8 volts, and the current doesn't surpass 5 amps. 


 

Right before your eyes, silver crystals start to grow. It is necessary to make sure that it doesn't grow to reach the tea filter, so that a short-circuit doesn't occur. Some people say that the reaction or growth of the crystals, goes 8 grams/amp , but in reality it goes slower, because part of the current goes to waste. The reaction is accompanied by an excretion of warmth, the blob dissolves, and crystals grow at the bottom of the electrolytic bath. The tea filter acts as a filter (obviously) for all the junk and slime, produced by the dissolving blob. 


 


When the reaction ends and the blob dissolves, we take apart the electrolytic bath, pour the silver nitrate into the chemical jar until the next use, rinse the newly born silver crystals in water a few times, then we filter and dry them. 


 


 After that we melt the silver and preform a normal water casting to acquire small sliver bits for any future projects. This silver that you see is .999 (pure) silver. We can now let out a sigh of relief, because there was a bit of fear while the silver was in a liquid state, because we could not touch it or see it.   :)


 


The calculation shows that we received around 473 grams of the 500 that was in the impure silver.


After diluting the silver in nitric acid, there are still some rouge fragments. The acid didn't dilute them and their make-up is unknown. :)





Until next time. :)