Troubleshooting and Optimizing Homemade Watercolor Mediums
Section 1: The Chemistry of the “Earth Pigment Problem”
The structural degradation of burnt sienna, burnt umber, and raw umber cakes in watercolor pans is a classic paintmaking challenge. While it is intuitive to suspect chemical iron oxidation over time, the root cause is entirely physical, stemming from the unique mineral structure and extreme absorbency of these specific earth oxides.
A standard gum arabic medium works beautifully for low-absorbency pigments (such as cadmiums or cobalts). However, earth pigments behave radically differently due to three core factors:
High Specific Surface Area: Earth minerals are highly porous and contain vast networks of microscopic cavities. This means they require significantly more binder by weight to fully encapsulate every single particle compared to heavier, denser mineral or synthetic pigments.
The Calcination (“Burnt”) Factor: Raw umber and raw sienna naturally contain chemically bound water molecules (hydrated iron oxides). When these pigments are calcined (baked) to produce the “burnt” variants, that structural water is driven out. This leaves the resulting pigment particles incredibly thirsty, causing them to rapidly draw moisture out of the binder as the pan cures.
Shrinkage and Brittle Tension: Because these pigments consume so much liquid, a standard volume of gum arabic binder leaves the dried paint film structurally starved. As the residual water slowly evaporates over several months, the gum arabic polymer network shrinks dramatically. Without sufficient plasticizer, this creates immense internal tension, causing the cake to warp, twist, snap, or completely self-destruct into a coarse, crumbly sediment.
Section 2: Modified Recipe for Earth Pigments
To fix this structural degradation, you do not need to alter your core master batch of watercolor medium. Instead, it is highly recommended to introduce pigment-specific additives on the mulling slab when preparing these difficult earth colors.
The Target Additives:
100% Pure Filtered Honey (Plasticizer & Humectant): Honey contains natural long-chain sugars (fructose and glucose) that physically wedge themselves between the brittle polymer chains of the gum arabic. This imparts incredible flexibility to the dried paint film, allowing the cake to shrink uniformly without snapping or warping away from the pan walls.
Extra Pure Glycerine (Humectant): Earth colors dry exceptionally hard and fast. A tiny amount of extra glycerine alongside the honey ensures that the core of the cake retains a microscopic level of moisture, preventing it from drying down into a bone-dry, dusty sediment.
The Slab Recipe Adjustment:
For every 1 tablespoon of your standard homemade binder used with Burnt Sienna, Burnt Umber, or Raw Umber, add the following directly to the mulling slab:
+ 5% to 10% Honey (Approximately $\approx 1/4$ teaspoon of runny honey)
+ 2 to 3 drops of pure glycerine
Section 3: Sourcing the Right Honey
In paintmaking, not all honeys are equal, and a highly processed, inexpensive grocery store bottle is vastly superior to raw, premium options.
| Property | Look For: Mass-Market Filtered Honey | Avoid: Raw, Unfiltered Honey |
| :— | :— | :— |
| Crystallization Risk | Extremely Low. Fine filtration removes all micro-particles. The honey remains liquid and smooth indefinitely. | High. Contains natural pollen grains and wax particles that act as “nucleation sites,” causing the sugars to crystallize into a gritty, crunchy texture that ruins the paint film. |
| Color Impact | Minimal. Light or Extra Light Amber clover honeys are translucent and will not muddy or discolor the subtle undertones of your earth washes. | High. Dark varietals (e.g., Buckwheat or Manuka) are opaque and can severely alter the transparency and tone of your colors. |
| Purity | 100% Pure Honey. Ensure the single ingredient listed on the back is honey. | Adulterated Syrups. “Honey blends” or flavored syrups containing high-fructose corn syrup make paint permanently sticky and attract pests. |
Paintmaker's Tip: If your honey begins to turn cloudy or sugary over time, place the glass jar in a warm water bath ($110\circ\text{F}$ to $120\circ\text{F}$ / $45^\circ\text{C}$) for 15 minutes to dissolve the sugar crystals completely before using it on the slab.
Section 4: Dynamic Performance Changes on Paper
Modifying your earth pigments with honey alters far more than just pan stability?it fundamentally changes the mechanics of how the paint behaves under the brush:
Increased “Open Time” and Flow: Honey is highly hygroscopic, meaning it actively pulls moisture out of the air. On paper, your washes will dry noticeably slower. This gives you an extended window to soften edges, manipulate pigment, and smooth out large washes without fear of creating premature hard edges or backruns.
Explosive Wet-into-Wet Dispersion: Honey acts as a natural surfactant, lowering the surface tension of water. When you drop a honey-rich earth paint into a pre-wetted wash, the pigment will charge forward rapidly, spreading out into beautifully soft, feathered, atmospheric clouds.
Enhanced Transparency and Glow: Gum arabic dries to a slightly satin, microscopic film that can sometimes appear chalky when heavily loaded with opaque earth oxides. Honey possesses a high refractive index; it bends light beautifully, forcing the light to pass completely through the earth pigment layer to bounce off the white paper beneath, yielding luminous, glowing washes.
The Trade-off to Consider: Honey drives pigment slightly deeper into the paper fibers, making the dried paint slightly more stubborn to “lift” or scrub away. Additionally, in highly humid environments, honey-heavy pans may remain slightly tacky to the touch.
Section 5: The Drawdown (Smear) Quality Control Test
Always perform this quick test at the very end of your mulling session to verify your binder-to-pigment ratio before scraping the paint into your pans.
Apply the Samples: Using your palette knife, transfer a small dab of wet paint paste from the slab onto a clean scrap piece of glass or clear plastic. Create two distinct patches side-by-side:
Patch A: A thick, opaque dollop (roughly the thickness of a coin).
Patch B: A very thin, scraped-down, transparent film.
Force-Dry: Use a hairdryer on a low, warm setting for 3 to 5 minutes, or place the test glass directly under a warm desk lamp until both patches are dry and cool to the touch.
Evaluate the Results:
[Thin Film: Rub Firmly with Thumb]
??? Pigment transfers to skin like chalk/dust ??? UNDER-BOUND (Add more base gum arabic medium)
??? Film stays completely locked down & clean ??? Successfully Bound! Proceed to thick patch check.
[Thick Dollop: Inspect and Scrape with Fingernail]
??? Glossy, glassy finish / snaps off in shards ??? TOO MUCH BINDER (Add a tiny pinch of raw pigment)
??? Overly soft / gummy / peels away like rubber ??? TOO MUCH PLASTICIZER (Add a splash of base medium)
??? Firm but flexible leather-like finish ??? PERFECT BALANCE! Safe to pour.
The Pour Protocol: Once your paint passes the drawdown test, pour it into the watercolor pans in shallow 1/3 layers. Allow each layer to dry completely for 3 to 4 days before adding the next. This phased approach completely eliminates uneven internal shrinkage tension, ensuring perfectly flat, structurally sound, and beautiful pans of handcrafted earth paint.