The Binder Blunders

Choosing the Right Binder for Gold Lustre Work

Gold lustre binders are the sticky medium that holds everything together before firing. Historically, potters made them from natural oils and resins mixed with sulphur. Smelly, volatile, short-lived and often noxious, these concoctions were used to suspend metal salts and adhere them to ceramic surfaces.

During the lustre firing, typically in a low-oxygen kiln atmosphere, the organic components break down and the metal species present are chemically transformed and deposited as a thin metallic layer. For copper and silver, this process requires a reduction environment in the kiln, which consumes free oxygen and forces the metal into its metallic state rather than forming a metal oxide.

Gold and platinum behave differently. A reduction firing is not strictly necessary, as these metals are more stable in their metallic state than as oxides. However, when using a resinate lustre, the carbon-rich binders tend to push the local surface of the piece into a reducing environment anyway, as the organic material burns away and scavenges oxygen during decomposition.

Modern analysis shows that the effect is not simply paint sitting on the surface, but rather a layer of metal nanoparticles trapped just beneath the glaze surface. (Usefzaei et al., 2023)

The potters behind Islamic, Hispano-Moresque, and Italian maiolica had no periodic table and no patents, but they discovered that certain sulphur-rich resins and oils worked as early binders. It’s tempting to equate these smelly brews with modern gold sulpho-resinates or mercaptides and there is a real chemical connection, but the tightly defined mercaptides we use today are a later, industrial refinement of that same sulphur-rich idea. (Chabanne et al., Ceramics with Metallic Lustre, 2011)

Those early recipes came with baggage:

• Short shelf life

• Gels or separates unpredictably

• Inconsistent performance

• Variable starting materials

• Required heroic burnishing for any real shine

In short, they were a glorious mess. Effective, yes, but fussy, temperamental, and wildly unpredictable. Definitely not something you’d want to brew in your kitchen unless you had a deep and active dislike of your neighbours.

In the early days of lustre glazing, these secrets were closely guarded, learned over decades and passed down to a very select few. This allowed apprentices to absorb the countless subtle variations in materials, timing, and kiln behaviour, helping them coax more consistent results from what was otherwise a thoroughly inconsistent process.

So What’s Changed?

Modern binders are about more than sticking gold to pots. They act as scaffolds, shields, and stage managers rolled into one. A good binder needs to:

• Form a smooth, cohesive film when applied

• Hold its shape as solvents evaporate

• Stay stable through the kiln ramp-up

• Burn away cleanly without residue

• Match the thermal behaviour of the gold compound

The Binder Trials

When starting my quest to find a suitable binder my knowledge hovered somewhere between nothing and very little. I had a vaugue idea of the properties required and came accross some interesting information. Many references to pine resin, gums, natural sticky oils, clay, ochre, honey, vinigar and even wine. But none of these would cut it for a modern approach, we need something pure, something stable a starting point than never varies.

Pine Resin (Colophony)

• A nod to history, used in early gold resinate formulas

• Romantic, easy to source, but inconsistent from batch to batch

• Made up of a mix of ingredients

• Not inert so hard to predict shelf life

I gave pine resin a wide berth at first, preferring something modern, stable, and less likely to throw a tantrum. But I’ll be circling back for two reasons. First, I’ve finally wrestled the rest of the ingredients into submission, which means I can now see what pine resin is really capable of without twenty other things simultaneously misbehaving. My early experiments were a blur of bad variables, when things went wrong (which they did, often), it was impossible to know whether the resin, the gold, or just my general impatience was to blame. Now, with everything else playing nicely, I can let pine resin take centre stage and see if it shines or sulks.

Second, it turns out pine resin doesn’t always have to arrive in its raw, sticky, moody form. There are processed versions that behave like civilised materials, consistent, repeatable, even predictable. The one that really caught my eye is polymerised rosin (sometimes dressed up as phenol-formaldehyde-rosin polymer), part of a whole family of “refined” rosins designed for stability and performance. In other words, pine resin with its rough edges knocked off.

Ethyl Cellulose

• Classic binder in pharmaceuticals, cosmetics, and food

• Forms a thick, brushable film

• Pre-fire films were uneven, lacked gloss and required complex solvent blends

• Taught me terms like coffee ring, coffee eye, sagging, orange peel

• Soluble and safe but unreliable for high-quality lustres

Those early tests? A glorious disaster. A mess. But just enough of a golden glimmer peeked through to keep me chasing it.

Once ethyl cellulose failed, I was out of ideas. My polymer knowledge hovered somewhere between nail varnish and Perspex. Back to the internet I went. That’s when I hit paydirt: a hidden universe of specialist polymers designed for precise, odd jobs, art restoration, palaeontology, not pottery, but perfect for sticking ink & pigments.

Enter the Paraloid Range

• Paraloid B67 (polymeric acrylic): strong, flexible, glossy film; excellent brushability; compatible with many solvents. Resulted in pinholes, surface defects and strange migration of the gold.

• Paraloid B44 (another acrylic): stronger film, burns away relatively cleanly; resulted in cracked, dull gold that required heroic burnishing like crocodile skin.

At this point I realised I couldn’t keep buying polymers like pick-and-mix sweets. Hundreds existed, most better suited for nail salons than pottery studios. I dug through safety data sheets and product specs, trying to make sense of the chemical jungle. None gave guidance on behaviour in a kiln. Until I cracked the code: the secret language of polymer thermal behaviour and why some are more suitable than others

The Thermal Language of Polymers

Key terms for lustre work:

• Tg – Glass Transition Temperature: when a polymer shifts from hard and glassy to soft and rubbery. Think warped Tupperware.

• Td – Decomposition Temperature: when it breaks down chemically, evolves gases, or leaves carbon.

• Tf – Flow Temperature: when the polymer softens and starts to flow, just before decomposition.

Tg keeps the scaffold firm, Td tells it when to bow out gracefully, and Tf prevents sagging. Armed with this I looked back over my tests with fresh eyes and started to read the issues i was seeing, paraloid b67 was melting and running in the kiln so the gold was migrating down the tile. B44 was drying, shrinking and cracking

Finding the Right Polymer

With this knowledge, I revisited patents and past experiments. That’s where Poly(isobornyl methacrylate) came in:

• Tg: ~190–210 °C

• Burnout onset: ~300–500 °C depending on heating rate and atmosphere

• Tough, hard coating

• Glossy, smooth flow when brushing

• Burns cleanly

It wasn’t cheap, the first quote was $600 per gram, which is why i skipped sourcing this initially, but armed with my new found confidence in its ability I got back to searching and found a somewhat more economical supplier as it provided the control I needed. The binder finally played nicely with the gold, the solvents, and the kiln. T he gold stayed exactly where it was applied and for the first time I was seeing bright continous golden films on my tests. I was extatic, 

Conclusion: Your Binder Is a Thermochemical Dance Partner

A good lustre binder isn’t just pretty. It needs to:

• Stay rigid until the gold is ready

• Decompose in sync with the gold

• Leave no trace

Early potters never had this control. Pine resin had its moment, but modern polymers let us fine-tune timing and consistency. We want lustre that works flawlessly, every time. Mirror-bright gold, no defects, no tedious burnishing.

Pine resin may still have a role, especially with gold thiol compounds. For now, everything else is finally in harmony, and I may revisit it later to see what this old material can teach me in a modern context.