Preparing the Treasure

The Gold

Gold. Not just a shiny metal but the true chemical chameleon of our lustre glaze. To keep things simple (and my blood pressure down), let’s start with a clean 2.5 grams of pure gold. This route skips the headache of purifying raw river gold and lets us dive straight into the alchemy.

Step 1: Making Gold Chloride

You’ll need:

• 2.5 g pure gold (small coin-sized chunk)

• 10 mL concentrated hydrochloric acid (HCl)

• 3.5 mL concentrated nitric acid (HNO₃) — aka the fearsome aqua regia mix

• A 250 mL glass beaker

• Magnetic stirrer and stir bar

• Hotplate with temperature control

• Fume hood (no exceptions—this stuff is nasty)

• Safety gear: gloves, lab coat, goggles, and maybe a backup prayer

Start by adding your gold to the beaker. Slowly pour in the hydrochloric acid, then carefully add the nitric acid to form aqua regia. The mixture will fizz and hiss—like a potter’s kiln on steroids. Set the hotplate to a gentle 50°C and place the beaker on it with the magnetic stirrer spinning at a low speed.

Within about 30 minutes, your gold should dissolve into a bright yellow-orange solution of gold chloride. If you see undissolved flecks after an hour, patience or a little more heat might help—but don’t boil it dry.

Why?
Aqua regia dissolves gold by forming gold chloride complexes—without this, that stubborn metal would just sit there mocking you. This step transforms solid gold into a reactive ionic form that we can work with chemically.

Step 2: Evaporate Excess Acid

Once the gold is dissolved, carefully transfer the solution to a larger 500 mL beaker. Slowly add about 200 mL of distilled water to dilute the acids. Set the beaker back on the hotplate at low heat (around 40°C) with stirring, and gently evaporate until the solution volume is reduced to about 30-40 mL. This concentrates the gold chloride while washing away excess acid.

Avoid evaporating to dryness here — the goal is a thick, syrupy solution, not a crusty mess.

Why?
Diluting and evaporating reduces the concentration of leftover acids which can cause nasty side reactions later on. It’s like giving your gold chloride a quick spa treatment to calm down before the next chemical dance.

Step 3: Reducing Gold Chloride with Methyl Sulphide

Now we get to the magic. Using a clean 100 mL beaker, transfer your concentrated gold chloride solution. For every 10 mL of this solution, slowly add 1 mL of methyl sulphide (dimethyl sulfide). The reaction forms gold(I) complexes and reduces the gold ions.

Keep the mixture stirred on the magnetic stirrer at room temperature for 15–20 minutes. You might notice a slight color change or cloudiness—that’s your gold molecules starting to get friendly with sulfur.

Why?
Reducing gold chloride with methyl sulphide prevents the formation of excess sulphides that would otherwise contaminate your final gold mercaptide. Think of methyl sulphide as the bouncer controlling the crowd—only letting in the right guests and kicking out the troublemakers.

Step 4: Forming Gold Mercaptide with Dodecanethiol

Next, add dodecanethiol (C₁₂H₂₅SH), roughly 1.2 times the molar amount of gold present (this usually works out to about 0.5 mL per 2.5 g gold starting weight). Add the dodecanethiol dropwise while stirring continuously.

This reaction forms gold mercaptide—a soluble, organo-metallic compound where gold is bound to sulfur chains. This is the star compound that will mix with your resin vehicle for painting.

Allow the mixture to stir for at least 30 minutes at room temperature under the fume hood. The final solution should be smooth and free of visible solids.

Why?
Dodecanethiol bonds to the reduced gold ions, forming a mercaptide complex that’s soluble in organic solvents and compatible with our resin system. This molecular makeover lets us paint gold onto pots like a pro instead of wrestling with dust or flakes.

Safety & Equipment Summary:

• Fume hood: Non-negotiable when handling aqua regia and volatile solvents.

• Personal protective equipment: Lab coat, acid-resistant gloves, goggles.

• Beakers: 250 mL and 500 mL borosilicate glass preferred.

• Magnetic stirrer and hotplate: For controlled heating and mixing.

• Waste: Neutralize acid waste carefully and dispose per local hazardous waste guidelines.

This multi-step dance takes raw gold through its transformation from inert metal into a chemically reactive, paint-ready gold mercaptide. It’s a mix of patience, precision, and respect for the chemistry — but once mastered, it unlocks the secret to that shimmering, mirror-like gold lustre that turns a humble pot into a treasure.