Because I don't have Rhodium metal on hand I'm forced to hopefully make an alloy of Lead metal and a 99.9% liquid Rhodium Chloride (RhCl) standard.
To accomplish this task I begin by cutting a 1 gram piece of 99.5% Lead from a small bar, which is hammered thin and flat. Then I curl up the outside edges to make what I refer to as a boat, as seen in the next image.

This image is showing the pipett dispensing a total of 2 ml of liquid Rhodium chloride into the Lead metal boat.
Each milliliter is supposed to equal 1 mg of Rh.
I suspect that some Rh will be volatilized as the propane torch heats the liquid.
No metal odor was detected as I drove off the liquid, but could certainly smell the chlorine.
Some caution is necessary to avoid melting the thin Lead edges and thus losing liquid.
When all the liquid has been dried the thin Lead is folded in half and folded again and again as shown below. Then this metal that now contains the residue from the liquid is hammered to somewhat seal-in this reside, so that when the lead is melted it will alloy with the Rh.

The next 5 images illustrate the melting and alloying (Pb & Rh) of the folded Lead metal boat.
Although these images are taken during the hot stage and will be significantly different when the plaster tablet has cooled they do provide sublimates of this heat range that when compared to Lead or other alloys will be slightly or vastly different and as a result will provide valuable clues for future reference.

I try to post a date on the tablets so that I might be able to recall the circumstances, as well as establish a time frame for reference.
I used to save all the plaster tablets, which became a major job, but found that not only did the sublimates almost vanish but the heated portions of the plaster began to crumble. So, establishing a digital library is the most appropriate way of saving images.

Even though this metal button is still almost red-hot significant fading has begun.

10x
This image shows the resultant cooled PbRh alloyed button on the above plaster tablet(s).
Colors of this cold plaster tablet are very close to accurate, excepting shadows and reflective light.
The reddish feathery glob on top of button is probably Lead oxide (Pb3O4) that forms easily when using a propane torch that blows considerable amounts of air allowing oxidation of the molten lead.
Direction of torch flame is from right to left.
So far there seems to be only minor differences between the other Lead buttons containing the pgms, and certainly not enough regarding the quantities involved to allow any sort of suggestion that a lead button may contain these goodies.
This button was removed from tablet, reasonably cleaned of adhering plaster and minor slag then cupelled as shown in following images.

The yellow sublimate color is the formation of Lead oxide. The red is a combination of Lead and other oxides contaminating this button (Ag, Rh and trace metals).
This and the following images attempt to demonstrate a simple cupellation procedure that anyone can do with a little practice. Once this methodology is employed there is no immediate need of having expensive electric/gas furnaces to accomplish the normal laboratory setting and task of obtaining precious metal prills from cupelling lead buttons of any size.
For those who may decide to learn to cupel I found that practice was my teacher.
Normally the position of intense heat would be a little lower below the molten lead button., but this time trying to view throught SLR of the 35mm 30 year old camera the hand holding the torch moved a little making the flame a bit too high.. My usual practice is to gradually heat the cupel with the Lead button already in place (within the cavity). so that the lead melts only when the bone ash below the lead button is sufficiently hot enough to begin absorbing the molten Lead. Furthermore, if too much heat (flame and force) is directed at the bead it will vaporize considerable amounts of the precious metals, as well as allow the cupel to cool below the heat range of absorption, causing the button to freeze. Over the course of much time, trial and effort I’ve learned a few tricks that only experience can allow while conducting this type of assay.
Prior to melting the Lead button I place a piece of silver under the lead so that the lead will absorb the silver and the Ag will act as a collector for the sought precious metals.

This image shows that the cupel, while still hot to the touch has cooled suficently to allow the brown stain to show around the resultant silver prill and indicating under these circumstances the high probability that no lead remains.

10x
Color of the prill is being influenced by the surrounding cupel stains.
The image shows the alloyed silver prill resting inside the cavity I previously dug out of the cupel to contain the original Lead button.
Although most of the molten lead is absorbed into the bone ash cupel a small amount is also vaporized and can be seen as wisps of smoke during the entire cupellation emanating from the lead button till near the end of the procedure.
I always save the used cupels if they have not been totally saturated with Lead. Usually, when I begin to re-use previously used cupels I scrape away any obvious contamination from the surfaces and only place the new lead button on/in a clean area to conduct tests like this, thus avoiding using new cupels. As long as there is a sufficient amount of uncontaminated cupel surface and the cupel does not crumble while scraping a new surface and cavity then small tests like this one works quite well.
Conducting cupellations like this will cause an unavoidable loss of some silver and possibly other precious metals. However, this method is a quick and inexpensive way to make reasonably accurate tests without having to resort to relying upon laboratory expertise.
Furthermore, if the prospector does not learn how to do simple tests then the prospector will remain at the mercy of those who capitalize upon ignorance.
Notice the minor crack below the prill. Cracks can be a source of considerable loss and avoided as much as possible. These cracks have likely occurred because of the unequal heat distribution over the entirety of the cupel.
There are unusual reddish orange stains and deserve further chemical scrutiny.

20x

40x
During what appeared to be the final stage of cupellation of the above prill it behaved weirdly, and I could see a film coating the molten silver bead. I was not at sure if this was the typical behavior of large amounts of Rh or if some other factor was in play. So, because of all my previous examinations of prills that showed signs of minor amounts of Rh I never once saw the behavior and appearance of such as this, consequently, it seemed advisable to re-cupel to determine if Lead was still present.
Sure enough, more lead was found, thus, somewhat partially explaining the odd behavior of this prill during the finishing stages.

10x
Direction of flame & sublimates (Pb & Ag) formation is from left to right indicating the direction by which heat was applied to this cupel.
Colors are accurate excepting shadows and reflected light on the prill.
There is an obvious grunge coating, which I have no idea what it may be. Perhaps, it is a chemical reactive combination of silver and Rh of some kind, that as far as I know is not supposed to occur.

25x
This view of the prill better illustrates the unusual surface features and will be an asset for making future predictive gestimates should this sight be seen again. The grunge coating is far more apparent. So far not a single silver prill that has been purposed contaminated with one of the pgms has sprouted. Sprouting of silver prills just before solidification is said to be a sign of purity, but I think sprouting is usually a sign of insufficient finishing heat.
This image also shows the brown of silver oxide better than the previous one. However, there is some other peculiar staining suggesting that it is possible that some Rh also oxidized in combination with the Pb & Ag. The point of this exercise is to scrutinize all events to get a slight grasp as to what is occurring to better be able to make future improvements where necessary.

40x
The curve surface makes it really difficult to focus over a broad area, so I tried to show as broad an area as possible at this magnification.

1-1-07, 11:55AM
The primary purpose of this portion of the assay is to determine what the crystal structure of the prill may appear like under the surface, as well as collect any metallic debris for further study.
To be sure that this AgRh prill was as clean as practical it was re-melted by the propane torch flame, which forced a draft directly upon the molten prill driving off any residual Pb. There were traces of Pb.
The bead size measures = .058" (diameter) or the equivalent of approximately 25mg or 25 ounces per ton if 100% silver.
Upon examination of the cupel -- not visible to naked eye, but at 40x there can be barely seen hundreds of tiny white metal spheres left in cavity where the prill was melted. This indicates that the torch blast was too strong, or that this RhAg alloy when melted may be spitting, which is a phenomena that I will have to try to examine.
While digesting this prill in nitric acid and chlorine free distilled water and heating till vapors rose there was a strong pleasant aroma of coffee.
Digestion was accomplished using 1 part HNO3 & 4 parts water.

20x top
Prior to acid digestion - On the bottom of this prill is a dark layer that appears to be metallic, which a portion is visible in this image.

40x
Same as top image, but double the magnification, better illustrating crystalline surface structure.

40x
Bottom of prill, with most of the rusty-black crust either dissolving or being sloughed off.

40x
12:33PM -- Due to the air bubbles that form during digestion the prill gets moved around a lot and the part of prill that had the rusty-blacks is not getting thicker as the silver is digested.
Minor heat has been applied to speed-up the acid reaction.

40x
Metallic blacks have fallen off the prill and are surrounding the prill (a tiny portion of and out of focus at bottom left corner) as it digests.
This prill rests on a glass slide that has a well (curved, concave or depressed area), so that the prill is contained in a relatively small area, and that this area will contain the 5 drops of solution w/o spreading all over the slide surface.
This solution vapors causes me to sneeze and I don’t like running acids next to pc , but no choice if I want to capture these images.
1hour has elapsed and the prill is only about 10% digested as seen in this next image according to window size.

40x
The black area continues growing or the silver is going into solution or both.
There is a slight pinkish color on the silvery prill.
1hr & 5mins lapse time.
There is also a yellowish-orange barely visible at edges of pic (out of focus) that looks like a thin film (oxide) that will peel off and float and sometimes sink to bottom of solution and rest with the black accumulated mass of what is likely Rh metal sponge.
Strong, but pleasant coffee odor as prill slowly digests.

40x
2hrs into digestion
The yellowish-orange-brown film and the black area continues to grow as well as the amount of blacks on bottom of glass slide-well.

40x
Brownish yellow orange translucent mass peeling-off of prill. I have no idea what this semi-transparent mass is, but apparently it is intimate with Rh under these conditions.
This magnification will not allow detail of these black masses of crystals, which upon higher magnification are more silver color than black.

50x
Black & silver metal
2:30PM the prill has completely digested.

70x
Image of above black mass, showing crystalline structures.

70x
More of the black & silvery crystals littering the entire area where the prill was digested.

70x of isolated metal crystal.
Higher magnification was not suitable.
Apparently this is the crystal structure of Rhodium.