3D WERK
PRINTED WAX · STONE-IN-PLACE
STONE-IN-PLACE CASTING GUIDE
Set the stones in the wax,
cast the metal around them.
Stone-in-place casting, also called wax setting, puts small stones into the wax pattern before it is invested. The metal is cast around them, so the pieces come out of the flask already set. Printed seats sized for calibrated stones suit it well, and it saves setting time on small stones. It only works if you choose the right stones and protect them with a cooler burnout and slow cooling.
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.
THE NUMBERS AT A GLANCE
1 to 3 mm
the small stones this method suits, about 0.33 to 10 points
630°C max
burnout with diamonds (Gold Star, SRS), not the usual 730°C
430 to 600°C
flask when you cast, the range across sources
Open
a hole under each stone, as wide as the design allows
No quench
cool in air until the flask is cold to the touch
WHAT YOU NEED
Calibrated stones
one lot, suited to casting
Heated wax tool
fine tip, low heat
Programmable kiln
with accurate control
Stone gauge
or micrometer, 0.01 mm
Stone-in-place investment
or the maker's additive
Pressure washer
or water jet for devesting
Loupe or microscope
to check every seat
Vacuum investing
mixer and chamber
Magnetic pin finisher
gentle near set stones
Before you start
Test with inexpensive stones first. Run a trial tree of low value stones of the same type through your whole process.
Plan a separate cycle. These flasks need their own investment, burnout and cooling, so they cannot share a kiln cycle with normal flasks. If a caster does your casting, agree the process first.
Record every temperature: kiln, flask and metal, so you can repeat a good result exactly.
WHERE IT MAKES SENSE
Many small stones. Pavé, channel, bead and prong settings. Stone-in-place suits small stones. Flashforge gives a range of about 0.33 to 10 points, roughly 1 to 3 mm in a round diamond.
Repeat pieces. Setting in wax needs less force than setting in metal, the metal is never hammered, and the time saved adds up over a run.
Heat tolerant stones of good quality, bought calibrated.
WHERE IT DOES NOT
Large or valuable stones. The risk to the stone outweighs the saving. Set them after casting.
Heat sensitive, treated or included stones. See the lists below.
No way to run a separate cycle. Without the right investment, burnout and cooling, the stones pay for it.
1
Choose the stones
Generally suitable
Diamond, natural or lab-grown
Well cut, few inclusions. Test colour-treated lab-grown stones first.
Ruby and sapphire
Natural or lab-grown. Not fracture-filled or dyed.
Garnet
Keep it away from hydrofluoric acid.
Cubic zirconia
No boric acid in the investment. Cool larger CZs extra slowly.
Some lab-grown coloured stones
Check with your supplier and test first.
Leave these out
Emerald*
Heat extends fractures and spoils fillers.
Quartz: amethyst, citrine
Change colour with heat.
Topaz, including blue topaz
Changes colour with heat.
Tourmaline*, peridot*, aquamarine*
Heat sensitive in most sources.
Opal, turquoise, lapis, jade
Crack, burn or change colour.
Pearl, coral, amber
Organic. They burn.
Treated, heavily included or fractured stones
Crack, cloud or change colour.
* Sources disagree on these. One Santa Fe Symposium paper lists emerald, aquamarine, tourmaline and peridot as castable, while Hoover & Strong list all four as unsuitable and Rio Grande and Flashforge each list three of them. Unless your caster has proven them, leave them out.
Quality first. Stones with inclusions tend to turn milky or frosty in the flask, and better quality diamonds are less prone to damage. Leave out heavily included or fractured stones.
Ask for untreated stones. Treated stones can change colour in the flask. Fracture-filled and dyed ruby and sapphire can be damaged even by mild acids, so pickling is a risk as well.
Lab-grown diamond behaves like diamond. GIA says its physical properties correspond very closely to natural diamond, so treat it the same way. Some coloured lab-grown diamonds, pink ones especially, get their colour from treatment after growth. Test coloured ones first.
Cubic zirconia casts well, with two cautions. Boric acid in the investment can discolour it, and larger CZs can crack because the girdle heats faster than the centre.
Diamond's main enemy in the flask is oxygen at high heat. In a burnout that runs too hot, the surface frosts or turns milky, and the damage is permanent. Step 3 covers the limits.
2
Set the stones in the wax
IN THE CAD FILE
A seat for every girdle. Model a groove in the setting for each girdle, so the stone sits level and is held above and below it. Prongs or beads should be fractionally smaller than the stone.
Open top and bottom. Rio Grande calls exposure to the investment above and below the stone absolutely required. Make the hole under each stone as wide as the design allows, and give every stone its own through hole. Ask your investment maker if they set a minimum.
Keep girdles apart. Metal shrinks as it cools and closes the gaps. Corners of square and baguette stones must not touch either.
Scale for the alloy. Alloys shrink by different amounts and can crush the stones. With printing that means a scaled file per alloy, proven by a test casting.
Least metal contact, most security. Sharp cornered stones need extra care in the design so the cooling metal does not break them.
AT THE BENCH
Measure the stones. One stone supplier quoted by SRS calibrates 1 to 3 mm stones to ±0.05 mm (CZ ±0.02 mm), and Flashforge specifies the WaxJet 51C to ±0.04 mm per 20 mm. Print a test strip of seats and fit your actual stones first.
Never force a stone. Injection wax guides rely on the wax flexing and springing back. Do not assume printed wax behaves the same. Flashforge softens the prongs with a heated wax tool so they close around the girdle. Practise on a spare print.
Check each stone under magnification: level, table up, fully in its seat. Then tap the pattern lightly. A stone that moves now will move in the flask.
Clean stones, clean hands. Grease or wax left on a stone is replaced by metal. Rio Grande dips the set tree in denatured alcohol. Try that on a spare printed pattern first.
Short tree, sprue into the heaviest section, away from the stones. Hoover & Strong recommend trees that fit a flask of 6 inches (about 150 mm) or shorter.
3
Invest and burn out
Use an investment made for stone-in-place, such as Gold Star GemSet or SRS Stonecast, or your maker's stone additive. These usually rely on boric acid, which helps protect diamonds from oxidation but can discolour CZ. Casting CZ? Ask the maker first.
Do not dose boric acid yourself. Added to a normal investment it thins the slurry, cuts setting expansion and makes breakout much harder.
Mix to the maker's ratio and vacuum invest. Dewax the way the maker says: Rio Grande and SRS steam dewax, while Gold Star says never steam dewax GemSet.
Lower the peak. Gold Star, SRS and a Santa Fe Symposium paper put the ceiling at 630°C with diamonds. Rio Grande allows up to about 650°C in a properly modified investment, Shor peaks at about 565°C and Hoover & Strong at about 430°C. Follow your investment maker.
Hold it longer. At a low peak the carbon from the wax is harder to clear, and leftover carbon means gas porosity. In SRS tests, 4 hours at 630°C was not enough and 6 hours was.
Cast into a cooler flask. Sources range from about 450°C (Jeweler's Alloy) through 490 to 530°C (Schuster) to 600°C (SRS). Hoover & Strong burn out at about 430°C and never let the flask go above about 454°C. Hold it there first: at least 1 hour (Gold Star), or at least 3 hours with 4 preferred (Rio Grande).
Shor: diamonds can turn milky above about 650°C in an oxidising burnout. GIA: diamond burns at about 850°C.
4
Cast, then cool slowly
Metal no hotter than the alloy maker says. Too hot turns diamonds white and leaves dark rims around stones. Rio Grande's starting point is 70 to 80°C over the liquidus for gold, 80 to 100°C for silver.
A fluid alloy and a strong, fast vacuum. Palladium or low nickel white golds, yellow and red golds, and silver are all used. The stones soak up heat, diamonds most of all, and the flask is cooler, so fluidity matters.
Never quench. Quenching a hot flask shatters or clouds the stones. Let it cool in air until it is cold to the touch: at least 1 hour (Jeweler's Alloy) or 2 hours (Shor), longer for big flasks and bigger stones.
CZ: Jeweler's Alloy puts the flask back in the kiln, switches it off and lets them cool down together.
You may read about quenching after 20 to 30 minutes. An SRS paper notes this is possible with small stones, but says flasks are normally left to cool completely. Start there.
After casting
Devest gently. Tap around the flask with a rubber mallet, then wash the investment out with a pressure washer. Expect it to break out harder than normal.
Check every stone under magnification for cracks, cloudiness, colour change and movement. Tighten loose stones by conventional means.
Pickle with care. Diamond shrugs off virtually all acids, fracture-filled or dyed stones do not. Jeweler's Alloy skips pickling and uses magnetic tumbling instead. Never use hydrofluoric acid: it attacks garnet and is extremely dangerous.
Finish gently. No high energy mass finishing or aggressive abrasive media near the stones. Magnetic pin finishing works well around them.
RISKS AND HOW TO REDUCE THEM
Diamonds milky or frosted
LIKELY CAUSE
WHAT TO DO
Too hot, or a normal investment
Cooler burnout and metal, the right investment
Cracked or chipped stones
LIKELY CAUSE
WHAT TO DO
Stones touching, fast cooling, flaws
Gap between girdles, slow cooling, clean stones
Colour change
LIKELY CAUSE
WHAT TO DO
Heat sensitive or treated stones
Untreated stones from the suitable list
CZ discoloured
LIKELY CAUSE
WHAT TO DO
Boric acid in the investment
Ask the investment maker which product suits CZ
Dark rim around stones
LIKELY CAUSE
WHAT TO DO
Unsuitable alloy, or metal too hot
Stone-in-place alloy at the maker's temperature
Metal over the back of a stone
LIKELY CAUSE
WHAT TO DO
Hole under the stone too small
Widest hole the design allows
Stones loose, moved or lost
LIKELY CAUSE
WHAT TO DO
Stones not matched to the seats
Measure stones, test-print seats, tap test
Gas porosity
LIKELY CAUSE
WHAT TO DO
Carbon left after a cool burnout
Longer hold at the peak, dewax as the maker says
Incomplete fill
LIKELY CAUSE
WHAT TO DO
Cooler flask, stones soaking up heat
Fluid alloy, sprue into the heaviest section
BEFORE THE FLASK GOES IN THE KILN: CHECKLIST
Suitable stones, untreated, clean
Seats test-printed for your stones
Open hole under each stone, as wide as the design allows
No girdles or corners touching
Every stone level, firm after a tap
Stone-in-place investment
Burnout within the maker's limit
Metal at the alloy maker's figure
Cool in air, no quench
Expect some losses
Even with everything right, some stones crack, cloud or change colour. Flashforge says manufacturers with strict process control typically keep breakage to about 1 to 2%. Price jobs with that in mind, and set large or precious stones after casting.
SAFETY
Investment powder contains crystalline silica, which can cause silicosis and lung cancer. Wear at least a fit tested P2 respirator when you handle powder and when you break the investment out. Clean up wet, never with compressed air.
Boric acid may damage fertility or the unborn child (H360FD). Follow its Safety Data Sheet.
Flasks stay hot for hours. Use tongs and heat resistant gloves.
WHERE TO NEXT
GUIDE 10 OF 13 · CASTING
THE BIG PICTURE
1 · DESIGN
2 · PATTERNS
3 · CASTING
4 · AFTER CASTING