Wednesday, July 18, 2007
Palladium is a strange element that present certain unique problems to the jewelry caster. Unlike gold, silver, copper, and platinum, palladium can absorb hydrogen for later release as porosity or other major casting flaws. Outcast does not contain volatile elements.
As a result, Outcast (or pure Pd) can be degassed by placing in a casting machine that has a vacuum pump. Pull full vacuum, then heat the metal to full flow temperature (usually indicated on a SEIT optical pyro at about 1380C). After the palladium is at full molten temperatures, shut off the heat and allow the palladium to freeze. Repeat once. This will also allow you to see how your pyrometer reads Outcast. Use your safety lens protected eyes to establish how your pyrometer reads Outcast. Each pyrometer is set for a different emissivity. So, palladium readings are only consistent on a given machine. After this process you may cast.
To cast-Flood the casting chamber with your neutral gas, (argon may be best) place the crucible, close up the machine, reheat to full flow temperature, and cast. We suggest full torque. We suggest substantial sprues. Experience in
A phenomenon we see is that the gases tend to move to the last part to freeze. So, sprueing is critical. Whatever is the last part to freeze happens to be, voids and shrinkage will often be found. It is not uncommon for large voids to show up in the button.
Questions? Call daniel
Friday, July 13, 2007
Thomas from Karen Jewelers in Tennessee called me and he described some issues about plating 950Pd.
I then spoke to Mark Mann (The official tech guy for PAI) and he mentioned good results with lower voltages, warm rhodium solution and extra care in the electro-cleaning stage. He may have worked out the oddities of rhodium plating 950palladium. This post has an important caveat-All 950palladium is not the same alloy. Only Outcast from PMWest was tested by Red Sky Plating successfully. I made no attempt to test TruPd or any other alloy. There are unknown variables here. The real answer as to why palladium is tricky to rhodium plate is not yet clear.
Thomas's note to Mark Mann used by permission-
I surely appreciate your call to me today; real conversation beats email in every way except to convey an image. The conversation may be beneficial to both of us. I did contact TechForm and that was a helpful contact.
The attached images are smaller file sizes than I could have sent but do show how we duplicated the "orange peel" or erosion of the palladium when rhodium plating is attempted. Remember, originally we duplicated the results with water and table salt as the bath.
Richard Knight did the odd formed piece of metal today and shot those photos. We had to violate every rule of jewelry photography to get the defects to show properly. Difficult was this with our "studio" of one desktop fluorescent lamp. Oh my, what a set up.
Details: This test was to duplicate the damage. Since there are many variables, the only definite conclusion is that damage did occur. Both the odd formed piece and the Hoover stock were polished to remove any traces of surface defects similar to the results shown. The odd formed piece is unknown PD950 alloy. We had one ring cast from wax by Platina and another cast from an "in-house" design by Unique Settings. Both of the castings were quite workable and nicely done. Unique did an extra fine job with theirs. The metal for the test today was taken from scrap of one of the items but we do not know which. We have no clue as to the alloys used by either Platina or Unique.
Rhodium was warm from previous use and temp was right at 100f. The Hoover stock was in the bath for 15 secs. at 2 volts. The odd piece was in the bath for 1 minute at 4 volts, a common time and voltage when we want a heavier plate on white gold.
I emphasized shadow detail a slight bit in Photoshop to allow the damage to be more clearly viewed. To the eye, the surface is cloudy and the pitting is not openly obvious. There is an obvious dull appearance due to the surface irregularities, an unacceptable condition for any item leaving our shop. You may let anyone you choose view or have copies of these photos for in-house use.""
One picture is attached of a failed attempt. Tip of the hat to Thomas at Karen's Jewelers, Oak Ridge, Tennessee for taking the time to submit the pictures of their attempts. I am very reluctant to name names of pictures of failed processes. Particularly until we have real confirmed answers to the mystery. It seems to me