Step-by-step formulation guidance using real ingredients and ratios
STOCK SOLUTIONS (DO THIS FIRST)
Before mixing a usable lustre, take the time to prepare a small set of stock solutions. This turns a messy, error-prone process into something accurate and repeatable, especially since you’re working with additions measured in milligrams.
I store these stocks in cheap amber dropper bottles. Nothing lab-grade, nothing fancy. Some live in 100mL bottles, with precious or low dose additions kept in 10mL bottles.
For very small quantities, drop-based dosing is often more reliable than weighing outside a lab environment. Once you know the weight per drop, it’s surprisingly consistent.
DROP-BASED DOSING CALIBRATION
Take your stock solution, then count drops into a small beaker on your scale until you reach 1.00g.
Divide by the number of drops.
Crude, yes. Effective, also yes.
For reference, the droppers I use give approximately 0.035g per drop for toluene and isophorone-based stocks. All drop counts elsewhere in this guide are based on that value.
UV TRACER SOLVENT STOCKS
These stocks are pre-dosed with Brightener 135, which makes the applied film immediately visible under UV light. They are used both directly in the mix and as the solvent for the polymer stocks, ensuring the tracer is carried through every component and ends up automatically in the final lustre.
UV tracer stock (toluene)
Bottle: = 100 mL
Brightener 135 = 300 mg
Solvent: = add 100 mL
Mix until fully dissolved. This is a fast- to mid-range evaporating solvent stock.
UV tracer stock (isophorone)
Bottle: = 100 mL
Brightener 135: = 300 mg
Solvent: = add 100 mL
Behaviour under UV is identical to the toluene stock, but evaporation is much slower. Useful for polymer stocks and for reducing drying stress. It worth noting the higher concentration of isophrone in the mix guves a thicker brush feel, less chance of dribbling, slumping and running when applied.
Bismuth stock solution
(If you followed my bismuth guide you will have this already).
Bottle: = 10 mL
Bismuth octoate: = 1.5 g
Toluene: = 8.5 g
Final mass: = 10.0 g
(15 % bismuth octoate in toluene)
Rhodium stock solution
Bottle: = 10 mL
Rhodium octoate: = 320 mg
Toluene: = top up to 10.0 mL
Final concentration: = 32 mg per mL
Polymer stock (PMIB + Rosin)
This stock is prepared using solvent drawn directly from the UV solvent stocks above, so the tracer is automatically carried through into the polymer and final lustre.
Final stock mass: = 10.0 g
Recipe:
PMIB (solid): = 3.00 g
Rosin (solid): = 0.75 g
UV solvent stock(s): = 6.25 g total
A simple starting point is a 50:50 split of UV-toluene and UV-isophorone. This can be tuned later to adjust drying behaviour but generally i find this a sane solvent mix in the final lustre.
Warm gently and stir until fully dissolved. PMIB dissolves slowly and does not reward impatience, so expect this to run overnight on a hotplate at around 30 °C. Loosely cover the beaker to minimise solvent loss.
It’s worth noting that higher proportions of isophorone slow dissolution further and lead to a thicker final solution.
WHY THESE STOCKS MATTER
The bismuth and rhodium stocks are pre-calibrated so that one drop is the correct amount for a 2g lustre batch. This fixes the weights at the beginning and removes the need to weigh vanishingly small quantities every time a batch is made.
THE RECIPE: PUTTING EVERYTHING TOGETHER ON THE BENCH
Batch size 10g
This example is for a 10g batch of finished lustre. It’s large enough to be genuinely useful, but small enough that mistakes won’t ruin your week.
What this recipe targets
Metallic gold: 11 %
Polymer solids: 15 %
Bismuth octoate: 0.26 %
Rhodium octoate: 0.07 %
Extra Solvents: blended from stock solutions
The order of addition matters here
Some components dissolve more cleanly in certain environments, others are easier to incorporate before the polymer is present, and the bismuth remains a little touchy and benefits from careful handling. The sequence below reflects the best compromise between all of these factors.
Before you start.
This recipe assumes you are working from the stock solutions described above.
Both the bismuth and rhodium stocks are calibrated so that one drop delivers the correct amount for a 2 g batch. For a 10 g batch, this simply scales to five drops of each.
All other additions, such as the polymer and any extra solvent, are added in the conventional way: place the vial on the scales, tare, and use a pipette to weigh in the required amount.
STEP-BY-STEP MIXING THE RECIPE
Charge the gold
Start with a clean glass vial, this is a one pot synthesis so this vessel will be the final contaner for your lustre. Weigh in 2g of gold mercaptide powderDissolve the gold
Add a 2.7g of your toluene UV stock solution to the gold vesselIntroduce the flux (first half)
Add 2–3 drops of bismuth stock slowly with stirring, slow stirring is essentialPolymer addition
Add 4g of PMIB/rosin polymer stock which gives 15 % total polymer solids in the final batch. Stir slowly until completely homogeneous.Complete the flux addition
Add the remaining bismuth stock, bringing the total to five drops. Staging the addition avoids local over-concentration and helps keep the system stable.Micro-addition: rhodium
Add five drops of rhodium stock. This looks insignificant. It isn’t.Bring to final mass
Top up with your solvent blend to reach 10.00g should be an additional 0.95g. Stir slowly and thoroughly.Warm and rest
Gently warm the vial to around 30 °C and allow it to stir slowly for a few hours. This isn’t about forcing reactions. It’s about letting the system to be well mixed. Allow the batch to cool and rest overnight before use.Test before committing
Before brushing anything you care about, pull a small test and watch the flow, drying and fried gold film. During application the lustre should show clear enough under a 365nm UV torch, the same type thats used for hunting minerals
NOTE ON TESTING
Throughout development, a small microwave kiln was used extensively for rapid testing. This allowed a film to be applied, dried, and fired to approximately 840 °C within minutes, using a pyrometer with a fine probe to track temperature. Each test took around ten minutes, making it possible to run dozens of firings in a single day.
That ability to test quickly had a significant impact on the research process, allowing a high degree of fine tuning over a very short period of time.