3D WERK
JEWELLER'S GUIDE · CASTING ALLOYS
CHOOSING A CASTING ALLOY
Same wax pattern,
a different metal.
The printer and wax are the same whichever metal you pour. The alloy is not. Carat, colour, hardness, melting range and even the investment you need change from one metal to the next. Here is what each common casting alloy asks of your workshop, and where to find the exact numbers for yours.
Before you start
This guide is general information to help you get the most from your WaxJet. It does not replace the Flashforge manuals, the safety data sheets for your materials or your own safety checks. Where they differ, follow the manufacturer's instructions and safety data sheets. Isopropyl alcohol (IPA) is highly flammable, and warm IPA gives off more vapour. Flashforge's manual uses a mix of PPG400, ethanol and IPA at 40 °C, never above 43 °C. Ethanol is also highly flammable. Keep it away from heat, sparks and open flames, heat it only with equipment suited to flammable liquids, use it in a well-ventilated area, and wear suitable PPE such as gloves and eye protection. Investment powder contains crystalline silica, and wax burnout and metal melting give off fumes, so use ventilation and the PPE your safety data sheets list. As a business, you are responsible for work health and safety in your workshop, including risk assessment and how you store, use and dispose of chemicals. See our Terms and Conditions.
01
Fineness and marks
05
Platinum and palladium
02
Yellow and rose gold
06
Melting ranges at a glance
03
White gold: nickel or palladium?
07
Recycling scrap
04
Sterling silver
08
Questions we hear
1
Fineness and marks
Carat counts gold in parts out of 24. US suppliers such as Stuller and Hoover & Strong call this karat (K). Fineness counts it in parts per thousand, which is what you stamp. To convert, divide the carat by 24 and multiply by 1000. Sterling silver, platinum and palladium use the same parts per thousand idea.
Why 585, not 583
Strictly, 14ct is 583 (14 ÷ 24 = 0.5833). Most makers followed the European practice of alloying 14ct slightly over, so the mark on most 14ct jewellery is 585.
The common marks
Gold 375, 585, 750, 916, 990 and 999. Silver 925 for sterling. Platinum 950, also 900 and 850. Palladium 950 and 500. These are common finenesses. ISO 9202 and AS 2140 list others as well, so check the standard.
Silver and the platinum group
925 means 92.5% silver, the rest mostly copper. Platinum 950 and palladium 950 are 95% of the named metal, with the balance chosen for casting or working.
Who stamps the mark in Australia
Australia has no government assay office, so there is no independent testing and hallmarking of the kind the UK has. The maker or importer is responsible for the fineness of what they sell, and stamps it themselves, usually with a maker's mark alongside. Australian Standard AS 2140-2008 sets out fineness marks in parts per thousand. Australian Standards are voluntary on their own, and only become mandatory when legislation calls them up. A fineness mark is still a claim about what the metal is made of, and the Australian Consumer Law bans false or misleading claims about a product's composition. So the number you stamp is your promise. Only stamp what the alloy and your scrap practice can back up.
Sources: State Library Victoria, Jewellery World, Standards Australia, Australian Consumer Law s 29(1)(a), World Gold Council, UK Assay Offices.
2
Yellow and rose gold
Coloured golds are gold plus silver, copper and a little zinc. The carat fixes how much gold is in the alloy. The balance of the other metals sets the colour and much of how the metal behaves at the bench.
Silver
Pales the colour towards green. It also matters for heat treatment: one Santa Fe Symposium study of 14ct alloys found about 7.5% silver was the minimum for age hardening.
Copper
Reddens the gold. Rose and red golds are copper-rich and harden by an ordering reaction. Copper-bearing golds, red golds most of all, tend to crack on further working if left to cool slowly after annealing. Water quenching keeps them soft and ductile.
Zinc
A small addition, typically about 2% and at most about 3% in 14ct to 18ct yellow. It deoxidises the melt, helps the metal fill fine detail and leaves a brighter surface as cast. It burns off a little with every melt.
Age hardening in brief
Many low and medium carat golds can be hardened with a low temperature heat treatment after casting or annealing. A World Gold Council paper shows 18ct alloys hardening at around 300°C. The effect can be large. One maker's 18ct red casting alloy is listed at 187 HV as cast and 336 HV after age hardening. Times and temperatures differ from alloy to alloy, so use the schedule on your alloy's data sheet, including whether to quench straight out of the flask.
3
White gold: nickel or palladium?
Gold is yellow, so white gold is gold bleached by another metal. As one alloy designer put it, you do not make it whiter, you make it less yellow. The two bleaching metals used in practice are nickel and palladium, and they behave very differently.
NICKEL WHITE
Hard, strong and lower cost
Hard as cast and work hardens quickly. More nickel gives a better white but a more brittle metal that is harder to pavé set or roll thin.
Melts higher than yellow of the same carat. Typical nickel white casting alloys: 14ct 940 to 977°C, 18ct 915 to 948°C.
Casts in normal gypsum-bonded investment. Liquidus sits below about 1100°C. One supplier advises flask temperatures at the high end of the range for white golds.
Prone to cracking. It can fire crack when heated, quench crack when cooled and stress corrosion crack in service, so follow the maker's annealing and quenching advice exactly.
Usually rhodium plated for colour, and it contains nickel, which some wearers are allergic to.
PALLADIUM WHITE
Soft, whiter, dearer
Soft and malleable. Pleasant to roll, engrave and pavé set, with no susceptibility to fire cracking.
Good colour and tarnish resistance. High palladium grades often need no rhodium plating.
Melts hotter. Published ranges run from about 950 to 1050°C for a low palladium 18ct to about 1100 to 1200°C for a high palladium 14ct.
May need a different investment. Once the liquidus passes about 1100°C, the hot metal tends to break gypsum investment down into sulphur dioxide gas. High palladium whites need a high temperature investment.
Costs more. Palladium is a precious metal in its own right, so the alloy is dearer than nickel white.
Rhodium plating is the norm for many white golds because it gives a bright, very white surface. Whether a given alloy needs it depends on its colour grade, which your alloy supplier can tell you.
Nickel, allergy and the EU limit
Nickel allergy is common. The Nickel Institute puts it at about 15% of women and 2 to 5% of men, depending on the page. The European Union limits how much nickel jewellery may release under REACH Annex XVII, entry 27: no more than 0.5 µg/cm² per week for items in direct and prolonged skin contact such as rings, earrings, necklaces and bracelets, and 0.2 µg/cm² per week for posts in pierced ears and other piercings, tested to EN 1811. If you sell into Europe, or a client has a nickel allergy, choose a nickel-free white alloy and ask your supplier for its test data.
4
Sterling silver
Sterling is 92.5% silver, and mostly copper for the rest. That copper is behind the two things jewellers fight most with silver: firescale and tarnish.
Firescale
Copper oxide that forms when copper-bearing silver or gold is heated in air. During casting it can reach well below the surface. Pickle removes the surface oxide but not what is inside. The only real cures are removing metal, by sanding or bright dipping, or covering it with plating.
Tarnish
Silver darkens when it reacts with traces of sulphur gases such as hydrogen sulphide in the air, and the copper in sterling takes part. No silver alloy is tarnish-proof. Some are simply slower.
De-ox casting grain
Firescale-resistant sterling casting alloys replace some copper with deoxidisers such as zinc and silicon. These form a passive oxide at the surface that slows oxygen getting in, so less copper oxide forms. They resist tarnish longer, but still tarnish.
Argentium silver
Argentium was invented by master silversmith Peter Johns at Middlesex University. It adds germanium, which grabs oxygen before the copper can and forms a protective film, so there is no deep firescale and any heat marks stay on the surface. It is more tarnish resistant than traditional sterling, though not tarnish-proof, and it can be heat hardened. Grades include 935, 940 and 960, all above the 925 sterling standard. The 935 and 940 grades (93.5% and 94% silver) carry about 1% to 1.2% germanium. Argentium is weak while hot: hold the flask for 15 to 20 minutes before quenching, as your supplier says, and never quench while it still glows.
Sources: Argentium Silver, Rio Grande (Argentium white paper and instruction sheet), Hoover & Strong.
5
Platinum and palladium
The platinum group metals melt far hotter than gold or silver. Pure platinum melts at 1768°C and pure palladium at 1555°C. The common platinum 950 casting alloys, with cobalt or ruthenium, melt between about 1680 and 1795°C, and one maker's palladium 950 casting alloy melts at about 1350 to 1380°C. That is outside what a gypsum-investment gold setup is built for.
A different investment
Platinum is cast into phosphate-bonded or acid-bonded platinum investment, which is much stronger and takes more heat and pressure than gypsum investment. Palladium 950 also calls for phosphate-bonded investment. Steam dewaxing breaks most platinum investments down, so follow that investment maker's dewax and burnout schedule.
Different melting kit
Induction casting machines are usually preferred for platinum because they allow atmosphere control and fast, safe melting. For torch melting, hydrogen and oxygen is the fuel of choice. One supplier's palladium guidance rules out torch melting altogether and calls for induction under vacuum and inert gas.
Safety at these heats
Platinum melting light is intense and harms eyes. Rio Grande advises lenses of shade 7 or higher, and one safety supplier lists shade 8 to 12 for melting. Use the shade your melting equipment maker recommends. Platinum ruthenium alloys can give off toxic ruthenium oxide fume when melted, so melt them with fume extraction and follow your alloy supplier's instructions.
Honest advice: if your workshop is set up for gypsum investment and a gold and silver melting furnace, platinum and palladium mean new investment, new melting equipment and new skills. Sending those patterns to a caster set up for platinum group metals is a sensible option. Printed wax patterns go to them the same way.
6
Melting ranges at a glance
Typical published melting ranges, from solidus to liquidus. Treat them as a guide to which kit and investment you need, not as settings. One supplier notes that each maker's casting grain can differ by 100°F (about 55°C) or more.
YELLOW AND ROSE GOLD
9ct yellow
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
375
Paler yellow
880 to 900°C
Gypsum-bonded
Only 37.5% gold, so the silver and copper balance has a big say in colour.
18ct yellow
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
750
Rich yellow
855 to 905°C
Gypsum-bonded
Age hardens with a low temperature heat treatment.
22ct yellow
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
916
Deep yellow
965 to 1020°C
Gypsum-bonded
The highest standard gold mark before 990 and 999.
18ct red or rose
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
750
Pink to red
905 to 920°C
(one maker's alloy)
Gypsum-bonded
Copper-rich. That data sheet says quench in water straight after casting.
WHITE GOLD
Nickel white
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
585, 750
White with a warm tint
14ct: 940 to 977°C
18ct: 915 to 948°C
Gypsum-bonded
Hard, prone to cracking, usually rhodium plated. Check EU nickel rules before export.
Palladium white
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
585, 750
White, better grades need no plating
About 950 to 1200°C by grade
High palladium grades: high temperature investment
Soft, no fire cracking, higher cost.
SILVER
Sterling
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
925
White
About 780 to 895°C
Gypsum-bonded
Firescale and tarnish. De-ox grain reduces firescale, and melts differently: one is listed at about 825 to 855°C.
Argentium 940
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
925 or 940
White
860 to 895°C
(940 grade)
Gypsum-bonded
Germanium stops deep firescale. Weak while hot, so quench only at black heat. Other grades differ: one supplier lists its Argentium sterling at 766 to 877°C.
PLATINUM GROUP
Platinum 950
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
950
White
About 1680 to 1805°C (cobalt and ruthenium grades)
Phosphate-bonded or acid-bonded
Induction or hydrogen and oxygen torch. No steam dewaxing.
Palladium 950
MARK
TYPICAL COLOUR
MELTING RANGE
INVESTMENT
NOTES
950
White
About 1350 to 1380°C (one maker's alloy)
Phosphate-bonded
Induction under vacuum and inert gas. Absorbs oxygen and hydrogen when molten. Other 950 grades differ, so check the data sheet.
Ranges from the World Gold Council (Corti), Stewart Grice, Jurgen Maerz and Mark Mann on Ganoksin, and published alloy data sheets and guides from Legor, Rio Grande, Hoover & Strong and Cynthia Eid (Argentium 940). Palladium white figures are for specific published grades. Your alloy's data sheet overrides all of them.
Pouring temperature
Set above the liquidus by a margin from the data sheet. One supplier's general guide for carat golds is about 55 to 110°C (100 to 200°F) over the melting temperature with vacuum assist, and about 30 to 70°C (50 to 125°F) over for centrifugal casting.
Flask temperature
Much cooler than the metal. The same guide suggests about 590 to 700°C (1100 to 1300°F) for small, detailed pieces and about 425 to 540°C (800 to 1000°F) for heavy pieces, with white golds at the high end. Some alloy makers go higher still, such as 550 to 650°C for some yellow golds. Never go above your investment maker's maximum.
Why the data sheet wins
Two alloys with the same stamp can melt tens of degrees apart. Pour too cold and fine detail misfills. Pour too hot and you invite gas and investment reaction. Use your alloy maker's numbers.
7
Recycling scrap
Sprues and buttons from your own castings can go back in the crucible, but not on their own, and not every kind of scrap belongs there.
Use at least half fresh metal. The common rule is no more than 50% scrap in a melt. Some go further for white and pink golds: one supplier suggests 75% new to 25% scrap for white gold, and a higher share of new metal for pink golds too.
Know why old metal goes porous. Casting grain relies on small amounts of deoxidisers such as zinc, silicon and boron to protect the melt. Zinc burns off with every re-melt, so metal melted again and again protects itself less and picks up oxides and gas. Moisture in the melt adds hydrogen, which comes out as gas porosity when the metal freezes.
Only clean scrap from a known alloy. Keep sprues and buttons from each alloy separate, and clean off investment and oxides before melting. Anything you carry into the crucible ends up in the next casting.
Keep solder and old jewellery out. A little solder goes a long way to cause brittleness, and old solder seams can contain lead, bismuth or antimony, which can ruin a casting. Old jewellery and bench scrap go to your refiner instead.
Protect your fineness mark. Scrap of unknown or mixed fineness can pull a melt under the number you stamp.
8
Questions we hear
Is 585 gold the same as 14ct?
Yes. Exactly 14 parts in 24 is 583, but most makers alloy slightly over and stamp 585.
Which white gold should I use for a client with a nickel allergy?
A nickel-free alloy, such as a palladium white gold. Confirm the composition with your alloy supplier's data sheet rather than assuming from the colour name.
Do I have to rhodium plate white gold?
Not always. It depends on the alloy's colour grade. Nickel whites and low palladium 18ct are usually plated. The best high palladium grades often are not.
Does Australia have compulsory hallmarking?
Not in the UK sense. There is no government assay office to test and mark your work. The maker or importer is responsible for the fineness and stamps it, usually with a maker's mark. The mark is still a claim about composition, so it must be true under the Australian Consumer Law.
Can I cast palladium white gold in my normal investment?
It depends on the grade. Lower palladium alloys melt in the gold range, but high palladium whites melt above about 1100°C and need a high temperature investment. The data sheet will say.
Why does my sterling go grey or purple when I polish it?
That is firescale, copper oxide inside the metal. De-ox casting grain, Argentium or a protective atmosphere while the casting cools all help, but once it is there it has to be removed with metal.
Can I cast platinum with my gold setup?
Not safely or well. Platinum needs platinum investment, induction or hydrogen and oxygen melting, and the eye protection to match. Sending platinum work to a specialist caster is a sensible option.
Does printed wax suit every alloy?
Yes, the same printer and wax suit every alloy. What changes is the investment, the burnout and the scale of your file, because alloys shrink by different amounts. Check each alloy with a test casting and follow your investment maker's instructions for that metal.
How much metal do I need for a different alloy?
It depends on density, which changes a lot between alloys. One maker lists its 18ct red at 14.7 g/cm³ and its 18ct green-yellow at 15.7 g/cm³, and one supplier lists Argentium at 10.3 g/cm³. Our metal weight calculator does the sums.
Where do the numbers in this guide come from?
Published alloy data sheets and technical papers from the World Gold Council, Ganoksin, the Santa Fe Symposium and metal suppliers. Always check the data sheet for the exact alloy you buy.
WHERE TO NEXT
From the alloy to a sound casting
Casting from printed wax patterns?
Tell us what you make and what you cast in, and ask us for sample prints.
GUIDE 11 OF 13 · CASTING
THE BIG PICTURE
1 · DESIGN
2 · PATTERNS
3 · CASTING
4 · AFTER CASTING