[John]

Hi Ann,

I’m unfamiliar with the Schminke medium of which you speak, but I can offer some advice on underpaintings:

It is indeed good practice to let the underpainting become touch-dry before adding the color layer on top. Otherwise you risk lifting the underpainting and/or getting the underpainting’s color mixed in with the colors you’re laying on top. I think it is ok to use some linseed oil to get a thinner layer, but keep it to an absolute minimum if possible. Then make sure you let the underpainting dry (do the touch-dry test where you place the tip of your thumb – not your thumbnail – onto the painting, then press down. If any paint lifts off or smudges, it’s not yet touch-dry).

[Ann]

Thanks, I know I have to use the Schminke medium instead of linseed, but I’m assuming also that it’s OK to use the linseed in the underpainting if I leave it to dry first.

[George]

Ann,

When working with metallic powders—especially bronze—it is important to consider adhesion, solvent sensitivity, and long-term stability rather than simply appearance.

First, regarding the underpainting: yes, it should be fully dry before applying the Schmincke Bronze Medium mixture. The bronze medium you describe is based on white spirits and coumarone-indene resin. It is a solvent-borne system, not an oil-based one. If you apply it over a still-curing layer, the solvent can soften or disturb the underpaint and compromise adhesion. Allow the underpainting to reach a firm, solvent-resistant dry state—meaning it cannot be moved or marked with light pressure.

For the undercoat itself, a simple oil paint layer bound in linseed oil is preferable. Avoid alkyds such as Liquin under the bronze layer. Alkyd films cure differently and can form a relatively closed, slick surface that may reduce the mechanical adhesion of the solvent resin bronze layer. A traditional oil paint underlayer—transparent yellow iron oxide or raw sienna, as you suggest—applied lean and allowed to dry thoroughly, is structurally sound.

Second, about using linseed oil to mix the bronze powder: I would not recommend it. Bronze powders are best dispersed in a solvent-resin system designed specifically for bronzing. Drying oil films encapsulate metallic particles differently and tend to dull the metallic effect over time. They also increase the risk of discoloration and uneven oxidation. The dedicated bronze medium exists precisely to control film formation and metallic sheen.

If the client wants the same visual character as the earlier works, then using the same Schmincke powder and its matching medium is reasonable. The coumarone-indene resin system is standard in traditional bronzing liquids and gives the sharp metallic brilliance you observed—often brighter than pearlescent mica powders, which scatter light differently and appear softer.

Your sponging method is acceptable provided:

• The underpainting is fully dry.
• The bronze mixture is prepared immediately before use.
• The layer is applied thinly to avoid solvent entrapment.

The mottled effect you achieved is largely due to variations in viscosity and uneven particle distribution, which can be recreated by deliberately under-mixing the bronze dispersion and controlling the application pressure with the sponge. That approach does not inherently compromise the film if the layer remains thin.

Regarding achieving an egg tempera–like separation effect in oil: you are correct that true tempera mottling results from density differences and rapid water evaporation. Oil does not behave that way. To approximate the effect in oil, you would rely on controlled scumbling, sponge application over a tacky yet set layer, or slight variations in the ground’s absorbency—not on natural pigment separation.

Given that you are now working on lead-oil-primed ACM panels, you have far more stable support than with the earlier stretched cotton canvas. Structurally, this is an improvement.

In summary:
Use a lean oil underpainting. Let it dry thoroughly. Apply the bronze powder in its intended solvent-resin medium—not in linseed oil. Keep the bronze layer thin. That approach will give you the closest match to your earlier works without introducing unnecessary structural risk.

Your instinct to practice the more elaborate Duccio-inspired surface work on smaller panels first is sound. The material discipline required for sgraffito and clay tooling is entirely different from that required for oil handling.

Best,
George

[Ann]

Thanks so much, George!. Being a member of the this group is the best thing I ever did.

-Ann