Yggdrasil/Per-Ove: I think it wonderful that you are plowing new ground and casting rhodium, which most in the jewelry industry use mainly as a plating metal on silver or gold alloys! However, you are asking for specific mold casting temps and metal melting temps from folks who generally have no experience in casting rhodium, which melts at a temperature far above even the melting temperature of platinum. (mp of pt = 1768 C, while mp of rh = 1964C). The differential between the melting point of the metal and the temperature of the casting flask (ādelta Tā) will vary, depending on many factors, including how long the flask has been out of the burnout oven, what is the cross-sectional area of the casting is, etc., so weāre in an āunknown zoneā without practical experience. Then there is also the issue of investment breakdown, which could occur above the melting point of platinum, if using investment material developed for use with platinum. I donāt know how anyone can give you a really good answer to your questions about casting at these temperatures except for people who have done it. Perhaps there are experts at some of the metal suppliers who have experience with this. Iām interested in the answers to your questions, but, as many of us, completely out of any experience in the temperature range in which you will be working. The hotter things get the faster they cool down, but thatās hardly sage wisdom! Iām watching this thread with interest!
Then thereās this from the casting house Hauser and Miller: <<It is generally recommended that you should cast at 100 Ā°F above the flow point of the metal to allow it to be thoroughly molten. Caution should always be taken to avoid overheating. As a rule, the mold should be 800 Ā°F to 1000 Ā°F below the melting point of the metal at the time of casting. The flask will cool approximately 100 Ā°F per minute after removal from the oven. Have everything ready and check your equipment before you start to melt to be sure it will operate properly. Melt the metal thoroughly and cast immediately. Overheating is often the result of malfunctioning equipment.>> Add to this the factor that the hotter a body is, the faster it cools off and youāre into quite a juggling act! I donāt think this is very helpfulā¦looking for someone who casts rhodium regularly, right? -royjohn
Thanks a lot royjohn.
The fishing expedition bears fruit 
My hope was, that there could be someone that had some experience or knowledge in the area, so Iām totally aware that Iām moving into a uncharted terrain.
Iām trying to prepare as well as I can.
And your post is confirming my ideas on how I was planning it.
I have found some investment with max recommended casting temperature of 2100C.
This seems to be my best bet for now, regarding flask temperature I was hoping to scale the Platinum temperature and increase it by approximately 200C
Crucible for the melt should be ok with Zirconia as Zirconium dioxide melts at 2715C
How about the influence of vacuum on melting temperatures on metals?
Are there any significant difference?
Regarding some of the manuals I have seen they recommend waiting for quite some time after burnout of the investment since the interior cools way slower than the exterior.
Canāt remember exactly how long now 
Add to this the factor that the hotter a body is, the faster it cools off and youāre into quite a juggling act! I donāt think this is very helpfulā¦looking for someone who casts rhodium regularly, right? -royjohn
Quite contrary, Iām very happy with your inputs.
Since I have started this project I have found that two that have been casting Rhodium rings.
One has retired and one is some how out of reach, maybe retired too. One in US and one in UK
So I didnāt expect to find someone with first hand experience, hoping yes but expecting no.
Regards Per-Ove
Hi Per-Ove,
Glad my casual remarks were helpfulā¦I do have to point out that I have no experience in casting, so my remarks were based on whatās available to me or you or anyone else who can use google, and I tried to make that clear in what I said. Iād hate to be responsible for a casting attempt that went wrong in rhodium when that metal itself is so expensiveā¦
I am waiting with curiosity to see if any casters will weigh in hereā¦which they havenāt yet, AFAIK. Iād make a couple of other suggestions to you. As far as investments to use, breakdown temperatures, etc., the suppliers, like Rio Grande, Contenti, etc., etc., could easily give you the specs on their investments and also tell you what the recommended mold temperatures are for casting in gold and platinum, from which you could try to extrapolate to casting at rhodium temperatures. Also, when Iāve had casting questions, I have gotten good information from metals suppliers. Their technical reps should have a wealth of knowledge about metal alloys and casting temperatures. My last comment is this: you mentioned vacuum casting in your last replyā¦I got curious as to whether platinum is cast with a vacuum system. As far as I could discover, platinum casters use a vertical centrifuge or an expensive pressure-vacuum system systemā¦I donāt see any mention of a typical vacuum system such as is used to cast silver or gold being useful for platinumā¦therefore, Iād assume that it wouldnāt work well for higher temperature casting of something like rhodium. Hope this is helpful, but do be aware that my knowledge is just from reading about jewelry casting techniques and not from actual extensive casting of precious metals. If you do end up casting a rhodium ring, I hope you will document what you do and share it here. -royjohn
Thanks royjohn!
You are just further up the road than me then 
I have found and are still finding information daily on the net.
But the danger is, when you have little knowledge it is hard to sift out the nuggets from the vast sea of information out there.
I have reached out to a couple of investment producers without any reply.
So Iāll try the same with metal producers then.
And I will never hold anything against anyone for hints, I still need to do my own homework.
But maps and roadsigns are welcome for my journey.
-Per-Ove
PS!
I will of course share the journey with the forum.