Modern Gold Compounds

Metal Mercaptides (Gold)

The unexpected heroes of the gold lustre revival.

Before we dive into clean decomposition curves and slick film formation, let’s rewind a bit — back to the swampy origins of lustre chemistry.

In the early days, potters and alchemists brewed up what can only be described as stinky sulphur-rich soup. Picture pine resin, elemental sulphur, a splash of gold chloride, and the optimism of someone who’s never used a fume hood. What they were unknowingly doing was flirting with the chemistry of primitive thiols and thioethers. These early stews probably did, at some point in their unstable lives, generate something vaguely mercaptan-like — enough to produce a gold-bearing oil that could cling to a ceramic surface and reduce during firing.

Fast-forward a few hundred years, and we’ve got better tools, safer labs, and the ability to isolate actual gold-thiol compounds with precision. That’s where mercaptides step in.

Why Use Mercaptides At All?

Because they work. And more importantly, they work well.

Mercaptides are:

• Pre-organised metal complexes — the gold is already chemically “held” in a usable state

• Pre-solubilised — they mix into your resin system without needing high temperatures or complex reactions

• Firing-activated — under heat, the organic bits burn away, leaving a clean layer of metallic gold behind

And here’s the clincher:

Unlike the old stewpot recipes — where gold was mixed into a witches’ brew of sulphides, resinates, and side reactions — mercaptides cleanly decompose in a narrow, predictable temperature band. That means:

• No sulphur stains

• No charred crust

• No need for tedious burnishing

Instead, you get a thin, even distribution of pure metallic gold. This narrow-band decomposition is the reason behind the mirror-like finish that modern lustres can achieve with so little fuss.

Oh, and here’s the surprise bonus:
Many mercaptides reduce to metallic gold at temperatures well below 200°C, which opens the door to gold decoration on plastics, wood, paper — basically anything you can gently bake.

Two Mercaptide Camps: Alkyl vs. Aryl

Mercaptides fall into two broad categories depending on the type of thiol you use:

🧪 Alkyl Mercaptides – The Flexible Film Formers

Long, waxy carbon chains. Think oils, not powders. These tend to be softer, more flexible, and harder to isolate as dry solids (they love to behave like golden snot).

Examples:

• Dodecanethiol gold mercaptide – Flexible, solvent-friendly, used in many DIY systems

• Octanethiol gold mercaptide – Slightly shorter chain, lower boiling point, similar behaviour

• 2-Ethylhexanethiol gold mercaptide – Branched, a bit more volatile, easier handling

These are great for applications where flow and film-forming are critical — like painting fine lines or printing thin films.

🔬 Aryl Mercaptides – The Crystalline Powders

Based on aromatic ring structures, these are generally more brittle, crystalline, and easier to isolate as a dry powder — which can make handling and storage simpler.

Examples:

• Thiophenol gold mercaptide – A classic, with a sharp decomposition curve

• 4-Mercaptobenzoic acid gold mercaptide – Has polar groups, can affect solubility

• Benzyl mercaptan gold mercaptide – Somewhere between aryl and alkyl, depending on conditions

Aryl mercaptides are less gooey and more predictable when you're aiming for consistent pre-fired film thickness.

A Note on Grapefruit Mercaptan 🍊

Yes, it exists. And yes, you can find it. In fact, when I first started hunting for thiols, grapefruit mercaptan popped up as a promising option — commonly used in fragrance chemistry and sometimes more readily available than traditional thiols. But here’s the thing: despite its availability, it’s not well documented in the context of gold mercaptide synthesis. That doesn’t mean it wouldn’t work — just that you’ll be on your own if it goes sideways. Proceed with citrus-scented caution.

Summary: Why Mercaptides Matter

• Cleaner firing with more consistent results

• Bright, even gold without needing to polish

• Lower temperature reduction opens up non-ceramic surfaces

• More controllable chemistry — once you’ve made the mercaptide, the hard part’s done

• Flexible formulation — you can tailor solvents, resins, and additives around the mercaptide