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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Sun Jul 31, 2016 5:07 pm 
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Ammonium chloride is fine to use with any alloy since it only acts on that portion of the metal that has oxidised. If you have a melt that is particularly awkward and difficult to clear (i.e. get a clean, malleable, casting from) another trick I have used with great success is to add the ammonium chloride, then add some red phosphorus. This is such a fierce deoxidiser that it gives a really good result. There are two problems with it, however, it can be difficult to get hold of (the chemists supplier will look at you as though are mad) and I amat can be positioned to not sure of the toxicity of the smoke. I usually use it with a furnace fitted with a tall chimney although I have an exhaust fan with an extendable duct that can be used to extract fumes directly outside. First try the skewer to deoxidise and let me know how you get on.


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Mon Aug 01, 2016 4:08 am 
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Thanks Alan. I'll grab a couple of different sized nozzles next week and some ammonium chloride.

The silver was definitely more brittle after it had melted and set than it was when I first cut it into small bits and dropped it in the crucible.


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Mon Aug 01, 2016 5:51 am 
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Yes, that is the effect of oxidised metal in the mix. Ammonium chloride and the carbon from a wooden stirrer will definitely help.


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Tue Aug 09, 2016 3:50 am 
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Ok, got the large nozzle for the propane torch. Haven't had much success tracking down ammonium chloride. I've asked at the hardware store, a swimming pool and spa supplier and a rural products supplier. Each of them looked at me slightly strangely when I asked an I felt obliged to quickly follow up with "no, I'm not making a bomb - it's for jewellery casting" :) So the hunt for it continues.

Tested out the large nozzle, it delivered a much bigger (and noisier) flame. Put the previously melted blobs in the crucible along with some more chopped up bezel strip and applied the flame. The silver melted quite quickly this time and was soon rolling around in a bright silver ball like mercury dropped on a table. Trying to keep the flame on it as I lifted the crucible toward the mold, I tipped the crucible up and as I did, the nozzle must have gotten closer to the crucible since it made a slightly alarming jet engine noise. Instinctively, I jerked the torch back and the flame left the metal just as I was pouring. The result was that he metal solidified before the whole lot could run out of the crucible, with some of it pouring into the mold and the rest staying in the crucible.

Image

You can see the top of the ring band, it was starting to fill the mold before it solidified in the crucible.

Image

So, I need to work on my technique :)

What surprised me a bit was how smooth and shiny it came out of the mold. When I watched them do it at the club, it came out coved in grey firescale. Here, there doesn't appear to be any firescale at all and it's not argentium, just ordinary sterling I think - if the whole ring had formed successfully, would there be any need to pickle if it looked like this?

Anyway, I can keep re-melting this lot down for practice until I get the technique right.


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Tue Aug 09, 2016 8:00 pm 
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Several more attempts this morning with limited success. I increased the size of the air channels and added more air holes but the silver is still solidifying before filling the mould. It's all pouring out of the crucible nice and liquid.

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Perhaps the mould is too thin? Perhaps there needs to be a greater mass of molten metal? The air holes all pump out smoke so they aren't blocked.


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Tue Aug 09, 2016 10:29 pm 
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Just had another go but was unable to melt the silver, the torch continually coughing and spluttering even with adjustments. Score so far, silver 4, Lefty 0 :(


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Fri Aug 12, 2016 3:07 pm 
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Not sure what the problem with the burner is, try increasing or decreasing the pressure from the gas tank. The reason your cast is coming out bright and shiny is that the Delft process seems to use an oil based binder, that strips most of the oxygen out as the metal goes in. I would say that the problem with the metal solidifying before it is all in is that you haven't got enough feed holes into the mould. Try cutting out the sprue hole (the big hole you pour the molten metal into) then inverting the top part of the mould and cutting 3 holes at 120 degrees to meet in the bottom of the sprue hole. Cut the air release holes as normal, then reassemble the mould and try that. Ammonium chloride should be fairly easily available, I buy mine from a jewellers tool supply house in Birmingham (U.K.). If all else fails, contact them and see if they will post some out to you, Suttons is the name, in Vittoria Street, Birmingham 18.
As a side issue, I put a trial film of casting on Youtube, "Sidereal Bangle Making" is the title, you may find it useful. Note that the process I use in this film is to cast gold into an iron mould and then roll and solder the casting, I find that this improves the physical properties of the metal enormously. If you are interested in the physics of it, let me know and I will expand.


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Fri Aug 12, 2016 6:48 pm 
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Cheers Alan. I tried expanding the size of the sprue hole and making extra air holes before I read your post. The result was better in that the silver over half-filled the cast, but still incomplete. I haven't tried again since, I'll go down and have another go today.

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The reason your cast is coming out bright and shiny is that the Delft process seems to use an oil based binder, that strips most of the oxygen out as the metal goes in.


Yes, the first thing I noticed when I opened the plastic bag of Delftclay is that it smells like linseed oil. I find it does actually stick to my hands a little more than claimed, but not enough to be a problem. Every cast so far - although unsuccessful because they are incomplete - has come out so bright and shiny that I can't see it ever needing to be pickled. Very smooth surfaces too, much smoother than I was expecting.

I think I sorted out the problem with the burner, I think I was just trying to feed it too much gas. I throttled it right back and it stopped spluttering and still produced a flame that melted the silver without difficulty.

I'll check out your youtube video and I'm always interested in the physics of things :)

Regards


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Sun Aug 14, 2016 7:25 pm 
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Checked out "Sidereal Bangle Making" on youtube - very informative Alan. Thank you.

Is that you doing the work?


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Mon Aug 15, 2016 1:15 pm 
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Indeed it is, you will note from the continual non-sequitur that I am a better jeweller than film star! Keep trying with the Delft process, sooner or later you will get it right and then you will be off. I was asked to make a "cartouche" style pendant for a friend, it took me 4 attempts, but I got it in the end and now they are no problem.
When I have a little more time I will put together some notes of the physics of casting and post them for you and you will know why I go round what may seem a roundabout route.
Ant luck with the ammonium chloride?


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Mon Aug 15, 2016 2:33 pm 
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No luck with either ammonium chloride or with casting :? My batting average does not seem to be improving here. I keep getting the same result, a one-third to half-filled cast. The metal seems to freeze the moment it makes contact with the clay.

I've gotten other parts of the process down pat ie, I've worked out the fine control necessary to feed the torch the right ratio of air to gas so that it now burns smoothly without spluttering, I can melt the silver to a rolling liquid ball quickly, it all leaves the crucible cleanly with no silver left stuck in there - actually filling the impression properly is the last thing still beating me.

Think I might watch the youtube videos of it again to see if there's some little technique I'm missing. I won't be giving up anyhow.

Maybe you're supposed to swear at it in Dutch? :)


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Fri Aug 19, 2016 9:37 am 
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Did you try multiple feed holes? How about a bigger head to the sprue to give more pressure into the impression?
Notes on casting physics - 1) all metals are crystalline, 2) all metals contain impurities (unless you have access to some very high tech kit), 3) crystal size is governed by rate of cooling. So, minimise the impurities (ammonium chloride, flux and carbon as a deoxydiser help here. Melt quickly. Pour into a "smoked" iron mould (a mould that has been heated, rubbed with beeswax and held over a candle flame to coat the internal surfaces with soot). The effect of this is to allow the metal to fill the mould without solidifying, then the metal, cooled by the iron, solidifies quickly. Impurities in the metal, which form weak points, are pushed in front of the solidifying metal until it meets another crystal, so, the more crystals you have, the more the impurities are distributed and the less they will affect the strength of the metal. Castings into moulds that do not cool the metal fast will have fewer boundaries and thus weaknesses that may become apparent on further work.
Keep me posted about the Delft castings.


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Sun Aug 21, 2016 10:34 pm 
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I wasn't quite sure how to approach the multiple feed holes, was trying to visualize it exactly.

I just have this feeling I'm doing something important wrong.

I don't intend to give up here. Ultimately, I would like to be turning out hand-made jewellery in which I have been involved every step of the way - I found the stone, I faceted/cabbed the stone, I made the setting and set the stone.

I've just been granted permission to fossick on another cattle run. So far as I know, there's only amethyst, smoky, citrine and rock crystal on the place but there may yet be other gemmy things hiding there. I'm faceting a couple of pieces of amethyst as a thank you to the owner's granddaughter who got permission for me - but I'd really like to be able make a nice argentium setting and give her a finished jewellery piece rather than just some sparkly faceted stones. It would be all the more special to her to have jewellery set with stones from her grandparents place.

I'll crack this thing yet.


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Mon Aug 22, 2016 12:00 pm 
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Multiple feed holes are simple enough, fill the bottom part of the holder with sand and tamp it down well. Force the pattern in about 7/8ths of the way, fit the top part of the holder and fill that up with sand and tamp it well. Cut the sprue, then separate the two parts (the marks in the body of the two parts will enable you to match them exactly on reassembly), then, working from the upper impression, use an 1/8th inch drill to make holes, at an angle, up into the bottom of the sprue from the impression of the pattern at 120 degree spaces (about, near enough will do). Then the metal will flow into each third and give a full cast, don't forget to put air vents midway between each feed hole.
Good luck!


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 Post subject: Re: Learning To Became Bench Jeweler
PostPosted: Mon Aug 22, 2016 12:28 pm 
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are you centrifugal casting it?

I also have an almost memory about using steam to cast. I forget what it was.

If the metal isw cooling that fast you probably do not have it hot enough

I found this on a site.

Note, the temp of silver as it melts will be constant intil it is all melted, then you can get it hotter.


PURE SILVER CASTING PARAMETERS

Melting Point - 962 degrees C./ 1762 degrees F.

Specific Gravity – 10.49 grams per cc. – 10.49 x Wax weight.

Casting range – 1050 to 1060 degrees C./ 1922 to 1940 degrees F.

Flask Temperature – Vacuum Cast – 1150 to 1300 deg. F. / 621 to 704 deg. C.

Centrifugal Cast – 1000 to 1100 deg. F./ 537 to 598 deg. C.

Flask Temperatures should be adjusted to the size and weight of the castings.


Note: Pure silver can dissolve many times its volume of oxygen in a molten state. A reducing cover gas or neutral cover gas is strongly recommended during the melting process to protect the molten silver. For high production casting, a small addition of lithium is helpful in removing dissolved oxygen.

No guarantees are made for the aforementioned procedures that are provided as information for United customers.

I know that for centrifical casting you have to hest the flask and then melt the silver, the hot flask helps the silver stay fluid until it is distributed.

Not sure about the delft process.

In my brass casting class, they had a method of making a two chambered mold. the basc mold.then a second one was added that you added the metal to. You had the mold with the metal down, and melted it in a furnace, then you inverted it and the hot metal ran into the mold. I think you left it in the furnace upside down for a few minutes

We were using lost was with a ceramic shell.


I still have a piece of your labardorite on the faceting machine, been distracted latly and have not been able to cut for a few weeks.

Good luck I am sure you will get there.


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