I wanted to understand why my tubes of Schmincke gouache behaved so oddly on a particular paper I’d been experimenting with in the studio — a sheet I had sized to a silky finish using a dilute animal glue sizing and a couple of coats of Chinese silk sericin mix (a workflow I’d been using to get a smooth, low‑absorbency surface for collage and ink). The same colours that behaved predictably on my usual 300gsm cold‑pressed watercolour paper suddenly felt more streaky, reactivated easily, and sometimes flaked when dry. So I ran a controlled studio test to isolate what was happening and to see whether this was something I could adapt to or should avoid.
Why I set up a controlled test
I like to keep experiments simple and repeatable. If a material behaves unexpectedly, it’s tempting to blame the paint — but the substrate often does more than we realise. I wanted to compare Schmincke artist gouache performance between:
- standard, sized 300gsm watercolour paper (my control)
- the same paper treated to a silk‑like, low‑absorbency surface (my silk‑sized variant)
My goals were practical: note differences in flow, drying time, colour value, reactivation (how easily layers lift), opacity, sheen, and long‑term adhesion.
Materials and setup
Keeping the checklist tight made interpretation easier:
- Schmincke artist gouache (several primary colours + Titanium White)
- 300gsm cotton watercolour paper (sized) — control sheet
- 300gsm cotton watercolour paper, same batch, treated to a silk‑sized finish — test sheet
- soft round brushes (size 4 and 8), flat wash brush
- pencil for registration, ruler, glass jar of water
- microscopic loupe (×10) for close inspection
- spray bottle for rewetting tests, hairdryer (low heat)
For the silk‑sized sheet I applied two light coats of a diluted animal glue solution followed by two coats of a homemade sericin/gel mix to deliver a noticeably smoother, less absorbent surface. Each coat was allowed to dry fully and the sheet rested for a week before testing.
Test procedure
I painted a grid of standardised swatches across both sheets to compare the same operations in the same order. Each swatch included:
- single wash (diluted colour)
- opaque block (straight from the tube)
- two thin layered glazes
- wet‑into‑wet blend
- dry‑brush texture
- edge lift test (spray and blot after drying)
I timed drying at room temperature (~20°C) and documented the behaviour visually and with notes. I also performed an adhesion check after four days: a gentle fingertip rub and then a light scotch‑tape test in an inconspicuous area.
What I observed
Here’s what emerged, side by side.
| Characteristic | Standard sized paper (control) | Silk‑sized paper (test) |
|---|---|---|
| Absorbency | Moderate; paint sinks slightly into fibres — predictable matt finish | Much lower; paint sits on surface, appears slightly more glossy |
| Drying time | Short; thin washes set within minutes | Comparable for thin washes, but thicker applications took longer to lose surface tack |
| Reactivation | Low to moderate — layers rewet but are more forgiving | High — even thin dried areas lifted readily with a mist of water |
| Blending (wet‑into‑wet) | Soft transitions, natural bloom | Tends to sit and bead, so hard to achieve smooth wet blends without pre‑wetting |
| Opacity & colour strength | Even, predictable opacity | Colours looked more saturated when viewed wet, but sometimes darker once film fully dried |
| Adhesion | Good; passes fingertip rub and light tape test | Variable — thin layers generally fine, heavy opaque layers occasionally flaked under tape |
Two particular surprises stood out. First, the silk‑sized surface made gouache colours appear slightly more luminous and glossy because the paint film didn’t sink into fibres; visually that was attractive but it also meant the paint remained more reversible (easily reactivated). Second, thick passes of straight tube gouache on the silk‑sized paper showed small surface cracks after drying and could flake under light abrasion — a sign that adhesion at the paint‑paper interface was weaker when the paper didn’t absorb some of the binder.
Why Schmincke gouache reacts this way
Schmincke artist gouache is formulated with a high pigment load and a binder that relies on both surface adhesion and slight penetration into the substrate to form a stable film. When paper is very absorbent, a proportion of the binder migrates into the fibres and the pigment becomes mechanically anchored. On a low‑absorbency, silk‑sized surface the paint cures predominantly as a surface film — this gives clearer colour and a more intense finish, but with two trade‑offs:
- the paint is more susceptible to rewetting and scratching because the binder has not penetrated the substrate;
- thicker layers form a more brittle film and can flake if they lack mechanical interlocking with paper fibres.
In short: less absorption = more surface film behaviour = greater reactivation and potential adhesion issues, especially with heavy applications.
Practical tips for working with gouache on silk‑sized paper
If you want to keep the silk finish for its smoothness and optical clarity, here are strategies that worked in my tests:
- Thin your layers. Apply gouache in multiple thin layers rather than thick opacities. Thin applications dry more reliably and bond better.
- Use a primer for heavy opaque passages. If you need thick coverage, prime the area with a thin layer of absorbent ground (e.g. an acrylic gesso or absorbent clear ground) in that patch so the pigment can anchor.
- Introduce a binder boost. Mix a tiny amount of acrylic medium or Schmincke’s ready‑made binder extenders into the gouache for areas that need extra toughness; test first as it can alter sheen.
- Accept reactivation and work with it. Spritzing is a great way to blend on silk‑sized paper — but expect previously dried marks to soften. If you want permanence, avoid overworking once a layer is dry.
- Fix carefully. A very light application of a workable fixative or a microcrystalline wax (test beforehand) can reduce reactivation — but fixatives can alter colour and sheen.
- Test the tape. If your work will be framed or handled a lot, do a discreet tape test and consider varnishing with an archival spray if needed.
An approach I now favour in the studio
For most pieces where I want the silk finish but also robustness, I’ve adopted a hybrid workflow: I reserve the silk‑sized surface for areas of delicate glazing, ink, or collage where optical clarity matters, and I use a thin absorbent primer under larger opaque gouache passages. I also switched to thinner applications straight from the tube and embraced more glazing techniques instead of blocking in heavy, opaque masses in one go.
Running this controlled test helped me stop blaming the paint and start designing my surfaces around what I wanted to achieve. Schmincke gouache is a lovely, responsive paint — on silk‑sized paper it rewards restraint and planning. If you try this yourself, keep the test simple, document what you do, and let the material teach you its limits.
