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Learning casting from scratch

Hello all!
I have no experience with jewellry and have a steep road ahead.
So far what I have done with respect to jewellery, is to design and 3d print a ring to my wife, so now I have to learn to build an investment mold and so on.
Naturally I have tons of questions, but will start gently I hope.

Are there an ideal delta temperature between the investment/mold and the molten metal?
(Small casts, less than one OzT)
Is it possible/advisabe to design/mix/modify your own investment?

Be gentle please :slight_smile:

Regards Per-Ove

PS!
I do hope this post are with in the correct topic, I was looking for a topic to introduce myself as it is done in the gold refinig forum, where I’m used to hang out, but could not find it.
I guess each forum has its own ways :slight_smile: -)

A good place to start (other than finding a mentor or a good workshop) would be purchasing a copy of Tim McCreights’ beautiful book “Practical Casting, A Studio Reference”. it is a very thorough treatment of the process, and should answer most of you questions. Additionally, it comes in a handy spiral bound edition that will lay flat on your work bench.

Thanks for the reply!
I will look into this, are there also any good online sources?
There are always a million things on the net, but it is hard for us newbees to sort out what is good and not.
Regards Per-Ove

Your original post mentions that you have no experience with jewelry, but you don’t mention what metal you want to cast. Assuming that your 3D print is in some form of wax that can be burned out, take it to someone who will do this for you. You are still left with the basic task of cleaning up the casting, polishing it and hoping that it fits. If you want to make jewelry, you might start with fabrication. It is a bit less tool dependent and many of the tools that you will acquire will be needed to finish a casting. Doing this you will get a feel for how precious metal behaves and how get it to do what you want (it doesn’t always). When I started out, now 47 years ago, I too was attracted to lost wax casting. Along with a lot of basic tools, I purchased a complete lost wax casting outfit. With the exception of the oven, it still sits unused in my shop along with a Hoover and Strong plating outfit. I have made a lot of jewelry since then. The only casting I do is with Delft clay. You can begin to get a feel for the basic casting process by working in Delft clay and you can buy kits for less than $100. You will still need some hand tools, some way to finish what you make and a torch. These are all things that you will need regardless of how you make jewelry. My brother and I both had the big advantage of a father to teach us the basics and tools to use until we bought our own. Try to find someone who will help you get started. Since you spell jewelry with 2 l’s, you may not be in a place with these resources, but local community colleges sometimes offer courses and, if you have a rock and mineral club nearby, there may be people making jewelry with the stones that they cut and the inclination to help others get started. Stick with it, look for help where you can find it, but don’t be shy. Ask whatever questions you have and people will try to answer them. Good luck…Rob

Thanks for your input Rob.

I’ll respond to your well worded advice step by step, so it will be easier to tie it together.

Your original post mentions that you have no experience with jewelry, but you don’t mention what metal you want to cast.

I’m a bit shy on this one, as it will probably result in a massive outcry, but here it is:

My plan is to cast the ring in pure Rhodium of reasons not important to this discussion.

I’m fully aware of the massive set of challenges regarding this (Maybe not all the issues but that there are massive obstacles.)

I know it has been done and have reached out to two that have done it, but one has retired and one does not seem to be accessible. Metal and stone has already been purchased.

Assuming that your 3D print is in some form of wax that can be burned out, take it to someone who will do this for you.

My Idea was to print it in wax, but so far I’m not happy with the finish, so i will polish and modify the print and make a silicone/rubber mold to cast wax models.

You are still left with the basic task of cleaning up the casting, polishing it and hoping that it fits. If you want to make jewelry, you might start with fabrication.

I think fabrication will be difficult regarding Rhodium, due to brittleness.

Correct me if I’m wrong :slight_smile:

There will be post casting soldering though, since the prong/stone setting mechanism has to be produced in an alloy soft enough to be formed without cracking.

Pt90Rh10 or Pt70/Rh30 are both standard alloys.

It is a bit less tool dependent and many of the tools that you will acquire will be needed to finish a casting. Doing this you will get a feel for how precious metal behaves and how get it to do what you want (it doesn’t always). When I started out, now 47 years ago, I too was attracted to lost wax casting. Along with a lot of basic tools, I purchased a complete lost wax casting outfit. With the exception of the oven, it still sits unused in my shop along with a Hoover and Strong plating outfit. I have made a lot of jewelry since then. The only casting I do is with Delft clay. You can begin to get a feel for the basic casting process by working in Delft clay and you can buy kits for less than $100. You will still need some hand tools, some way to finish what you make and a torch. These are all things that you will need regardless of how you make jewelry. My brother and I both had the big advantage of a father to teach us the basics and tools to use until we bought our own. Try to find someone who will help you get started.

I did reach out to a few jewelers locally to help design the model, they just gave me a confused face and shook their head and that was just the model.

Since you spell jewelry with 2 l’s, you may not be in a place with these resources, but local community colleges sometimes offer courses and, if you have a rock and mineral club nearby, there may be people making jewelry with the stones that they cut and the inclination to help others get started.

Just recently I have located a local Silver smith where you can join in and at least watch them work. By the way you are right I’m from Norway so my language will have some glitches here and there :slight_smile:

Stick with it, look for help where you can find it, but don’t be shy. Ask whatever questions you have and people will try to answer them.

The craziest thing is that my current plan is to produce one ring, of course if it is successful, I may or may not continue if there is a sufficient market here.

Good luck…Rob

Thanks a lot, I probably need it

Regards Per-Ove

I don’t know much about rhodium. What I do know is that it is very expensive, and if you do find it, it will likely be plated on finished jewelry. It is also fairly brittle and probably needs to be alloyed with something else. Good luck…Rob

You are right, its main use in jewlery is in plating, due to its hardness and reflectivity.
It has a melting point of 1964 centrigrade and is quite hard at 6.0 Mohs
So it takes polishing quite well I guess.
These special circumstances leads to a few challenges.

What to use for Crucibles, what to use for Investment and so on.
How much over melting point is neccessary for fluid casting?
How hot does the flask need to be.
I’m shooting from my hip and guessing/hoping that a single ring investment will survive the hot melt and rapid cooling long enough for the metal to fill and solidify before crumbling totally.
I will of course need to test.

I did like Glenn suggested and bought the “Practical Casting, A Studio Reference” from Kindle.
It had quite some interesting information, but left some lacking regarding to PGMs

My plan so far, is to buy a High Frequenzy Induction furnace. They can be had for approximately 1000USD in Ebay for a 15KW 100 kHz unit.
They will need some hefty modification to add a vacuum chamber, modified coil and doesn’t come with the cooling. Besides that it should be ok, they have been recommended from co-members in GRF as quite acceptable.
My timeline is to finish the modelling/print around Christmas time and hopefully cast a year later.
So I’m giving myself a years time to learn and if I need more I can give myself more, but deadline is spring 2022 :wink:

Goddag Per,
Rhodium is higher in melting temp than platinum. That 400 degrees Fahrenheit is quite a bit in casting. No wonder jewelers looked at you funny. Read up on Platinum casting, and find a platinum jeweler. It’s a good starting point to have someone who works in higher temp casting to talk to. Normal casting of non platinum metals is not as finicky.

I have cousins in Haugasund Norway. Where do you live?

Aggie, born in Horsens Denmark

God kveld Aggie.
As you see from my previous post, I know the charteristics of Rhodium :wink:
I’m having trouble relating to imperial measurements so I stick to metric :smiley:
When referring to the latest info I found with Rio Grande and others, Platinum are cast at 1800-1900 deg C which is 32 - 132 over melting point and if Rhodium is behaving the same I should not need to go beyond 2200 deg C and then a Zirconium dioxide crucible should be ok. Rhodium is a bit lighter than Platinum but by making the sprue short and thick with good branching I hope it will be ok.

Regarding the Jewelers here I did not disclose the metal, I just asked if they could make a model or assist me making one. It seem it is so industrialised here now, that almoste no one actually do anything with respect to production and even hardly repairs anything.

I live in Bergen 2ish hours north of Haugesund.
Hilsen Per-Ove

Edited for precision of language.

I’m ready to start asking specific questions now.
How do one best do that in this forum?
Is it recommendet to start a new topic for each question for cleanliness and correlation, or is it recommended to keep it all wrapped in one topic?

Regards Per-Ove

Why not start with the beginning. The model you are making. Sounds like you are 3D printing it. Many here do that. I’m old school with some dentist like tools, wax, and an alcohol lamp. How intricate are you making the model? If done right I don’t see a need to make a mold unless you want to make future copies. Are you going to set stones in it? If so what type of stones, and what type of setting?

Everything else you want to do starts from making the mold. Then how to spruce it correctly. Most mistakes come from design and improper sprueing. If you have a year to work on this there is plenty of time to get it right

Till Lykke. Aggie

Sprue not spruce

Takker for det Agnes.
I’m 3D printing the base model, but I’m not happy with the finish/resolution, so I will add a layer of lacker then do some minor corrections and polish.
And then I’ll make a mold in silicone RTV so I have the possibility to experiment with it.
It will have 3 stones and the clasping mechanisms will be soldered on after casting.
They will be made of a Pt/Rh alloy so they have the ductility and strenght to hold the stones without cracking.
The main stone and metal have been aquired.
I was quite lucky with the Rhodium, I bought it just after it had jumped from 600 to 950 dollars TOz, I felt quite unhappy then, but with todays prices …
I’ll post the progress when I get there.
Regards Per-Ove

Hi again!
Due to lack of comments regarding thread and topics, I assume it is proper and ok to continue my journey in this thread.

Here it comes, I will start with temperatures:

Temperature:
Are there a set tempertaure gradient one needs to reach to get a fluid and good pour of the melt?
Like a percentage over melting temperature or x*100 centigrade over melting?
I found some online references that says 1800-1900 centigrade for Platinum and 870-970 for investment temperature.
Due to my lack of experience I’m not capable to assess these data properly.
But are a temperature of 30-130 centigrade over the melting point really sufficient?
Or is it a compromise that has been made to work?
Are there a set temperature gradient between the melt and the investment temperature?
The same source indicates a delta T of around 1000 centigrade between the melt and investment.
Is this suffcient or governed by the desire for long flask life?
Which is best, a high difference that creates a fast cooling or a low difference which gives a relative long time for cooling.
Sharp cooling or even a cooling shock, would of course give an opening for lesser quality investments but on the other hand, it may result in a lot of issues with the cast itself, like underfilling , bubbles, cracking and what not.
Besides optimalized sprues and channeling are there some tricks here?
I guess my lack of experience are obvious, but please comment and be honest.
If someone can point me to good information on the net I would be happy to read and learn.

PS!
I do not know all the proper naming conventions so please correct as needed.

Regards Per-Ove

You will soon learn to work by eye. I work with centrifugal caster and oxy-natural gas. YOu will learn the difference between metal just slumping and metal that is ready to cast. I use flux and a carbon stick. After the metal has started to pool and the flux is added I stir with the rod gently. Once the metal is melted and looks like a mirror it is time mto cast. This process is very forgiving. Most metals like silver and gold are easy. Some alloys have problems with overheating. I would check at rio-grande for more info.

Thanks for the reply Steve.
I’m talking about PGMs like Platinum and Rhodium, and I guess the margins between what the infrastructure can handle and what is needed may be quite narrower then.
And flux are never used in these temperatures.
So how much more than melting is needed in order to get a fluid melt?
Is it just tens of degrees centigrade or hundreds, or is this as anything else dependent on the material to melt.
What is most common?

I believe you are referring to the solidus and liquidous temperatures that are used for alloyed metals. There is quite a bit of information online explaining these. In addition, pure metals have only a melt temperature.

https://blog.lucasmilhaupt.com/en-us/about/blog/liquidus-and-solidus

Liquidus vs. Solidus - Lucas-Milhaupt

Liquidus vs. Solidus Simply put, liquidus is the lowest temperature at which an alloy is completely liquid; solidus is the highest temperature at which an alloy is completely solid. Pure metals are fluid, and they melt at a single temperature. For example,
silver melts at 1761°F (961°C), and copper melts at 1981°F (1083°C).

Thanks Cliff.
I was aware of this, even if I didn’t know the terminology.
There are still a lowest temperature that a given metal or alloy are transforming into a liquidous phase.
How much more, are the alloy/metal needed to be heated, to be at a temperature where it reaches a vicosity suited to be poured into a mould for casting?
Are it sufficient to get a few tens of degrees centigrade extra?
A table from an investment producer indicated 1800-1900 centigrade for platinum which is just 32 degrees from melting point at its lowest.
Is this really sufficient?
This would then mean that the casting temperature of Rhodium should be around 2010 degC
Will a vacuum chamber significantly change the melting point of metals?
It does with water :wink:

Regards Per-Ove

Sorry folks, I have to correct a significant miss wording :slight_smile:

It was supposed to be:
There are still a lowest temperature that a given metal or alloy are entirely transformed into a liquidous phase.
Regards Per-Ove