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Getting to the Core of Inpainting with QoR

Prelude

QoR Artist Watercolors (QoR)—commercially available water-soluble paints made of pigments dispersed in Aquazol (poly[2-ethyl-2-oxazoline]) resin—have progressively gained traction with conservators across specialties since they were introduced by Golden Artist Colors, Inc. (Golden) in 2014. I recently chose QoR to inpaint a Modern Canadian oil painting that had an alcohol-sensitive partial coating. I used it straight from the tube, with deionized water as my diluent. I found the material tricky to work with—it felt sticky, I was unable to control the gloss and transparency, and my inpaints picked-up easily. This experience led me to question if there were tricks or techniques to manipulate this product more optimally. Luckily, some conservators have developed helpful tips for QoR, and they generously shared them with me for this article. (Note: This article is not sponsored by Golden, and there is no conflict of interest to declare.)

Background

Since the 1990s, conservators have been using Aquazol as an inpainting medium, typically for modern paint surfaces and painted objects (Golden 2014). Aquazol is available in four grades: 5, 50, 200, and 500, names which denote their molecular weights and indicate their viscosities (e.g., 5 has the lowest molecular weight [5,000 g/mol] and the lowest viscosity; 500 has the highest molecular weight [500,000 g/mol] and the highest viscosity) (Arslanoglu 2004). Eventually, several conservators approached Golden with the resin, suggesting that the company explore making a watercolor product with it (Golden 2014). Paint chemists there were impressed with Aquazol’s pigment loading as well as the thickness and quality of the film produced—the paint film resisted cracking and peeling through rounds of humidity-cycle testing (Jackson pers. comm.).

The resulting product, QoR (from the technical acronym for “Quality of Results”), are ready-to-use paints packaged in tubes (Figure 1) that are primarily sold and used as artist watercolor paints. The paints are comprised of pigments mixed with Aquazol and proprietary surfactants, compounds that wet and disperse pigments, and slow evaporating solvents that keep paints from drying out in their tubes (Jackson pers. comm., 2023). Golden does not disclose the specific Aquazol grades used in QoR, but it is believed to be blends of low and high weights that vary depending on the pigment (Jackson pers. comm., 2023). The extensive range of colors offered in the QoR series (presently 96) means mixing paints to color-match can be kept to a minimum, a significant benefit to conservators. The paint dissolves easily in water, alcohols, and ketones (specifically acetone), and it is relatively insoluble in aliphatic and aromatic hydrocarbons. Golden also performs ongoing, rigorous testing for pigment lightfastness and paint performance (Jackson pers. comm., 2023).

Aquazol’s water solubility is its main advantage over many resin-based inpainting systems. It does not require solvents that can sensitize modern paint surfaces or need air extraction – a convenience for onsite work. The refractive index (RI) of Aquazol at 1.52 (CAMEO 2022a) is higher than other water-soluble inpainting media, such as watercolor (i.e., gum arabic, RI of 1.46) (CAMEO 2022b) and egg tempera with an RI of 1.346 (Egg Tempera 2021). Aquazol’s RI is closer to other commonly used resin-based inpainting media, like Paraloid B-72 (RI=1.48), Regalrez 1094 (RI=1.52), and Laropal A 81 (the medium in Gamblin Conservation Colors, RI=1.53) (Berns and de la Rie 2003), and it has an analogous plasticity to these. All the higher RI resins present similarly—in depth, vibrance, and luminosity—to each other and to the surfaces conservators are trying to match; if correctly manipulated, QoR can simulate a range of mediums from oil, alkyd, and acrylic to encaustic and silk screen paints.

Medium, Palettes, and Swatches

James Bernstein, a freelance paintings conservator based in San Francisco and instructor of the “Mastering Inpainting” workshops, regularly uses QoR and has developed techniques for handling it. To begin with, he never uses QoR paints straight from the tube. Very slow-evaporating additives that prevent paints from hardening in their tubes make freshly squeezed paints slippery and slow to dry. This can cause inpaints to remain soft for weeks, vulnerable to imbibed grime, smearing, or transfer to another surface. Bernstein suggests squeezing out dabs of QoR paints and QoR Watercolor Medium onto a palette (preferably grey Plexiglass, specifically a lighter grey for modern and contemporary paintings and a darker tone for Old Master works, Figure 2) or into watercolor half pans.

 
Once applied to a palette or in half pans, he recommends leaving the paints to dry out for several weeks, in a dust-protected environment. This process allows volatile additives to evaporate from the paint, making it much easier to handle.

Creating palettes and half pans allows QoR tube paints to be shared between multiple conservators, offsetting the initial cost of buying an extensive set of paints. Golden’s GRIPR tube opener and a tube wringer (Figure 3) help facilitate sharing, in addition to reducing waste. QoR tubes should be stored in airtight containers to ensure paints remain fluid for longer.

Debra Evans, a retired paper conservator who co-instructs Mastering Inpainting workshops, recommends painting out swatch cards to keep alongside palettes and half pans as color references (Figure 4). Ivory matboard can be used for most colors, while grey matboard can assist in determining the relative warmth or coolness of colors. Each color swatch should have three applications of paint: a dilute wash, a middle level of saturation, and a fully saturated band. Swatches should be painted to the outer edge of a card, so that they can be placed next to an area in need of inpainting, and, therefore, aid in selecting inpainting colors.

Preferring to work outside the constraints of a metal watercolor box that holds 48 half pans, Bernstein makes spacious stepped Ethafoam blocks to arrange his QoR-filled half pans according to chroma and value (Figure 5). Using a table saw, he creates channels for the half pans and then tones the Ethafoam a light grey color with acrylic emulsion paint. In addition to directly labeling the half pans with permanent marker, Bernstein prints out the names of each color (using Excel, FileMaker Pro, or Word) onto heavy paper stock, and above each name he paints out a swatch of the color. The labeled swatches are kept with the half pans, adhered to the stepped Ethafoam block. By using this method, paint colors, which can look similar, or even indistinguishable, in the half pans are readily identified (Figure 6).

Figure 5. Side view of QoR-filled half pans in a stepped Ethafoam block, painted light grey, with labels and swatches adhered to the block.

Figure 6. Front view of QoR-filled half pans in a stepped Ethafoam block, showing the labels and swatches adhered to the block.

Bernstein points out that dabs on a palette can be easily rinsed if there is color contamination, while half pans may be more challenging to cleanse, as rinsing can drive contaminate paint further into the receptacle. Dried palettes can be wrapped in silicone-coated paper and stored in resealable polyethylene envelopes; half pans in stepped Ethafoam blocks can also be protected with a silicone-coated paper cover.

Pigments

Within the QoR set currently produced, Bernstein highlights the quinacridone pigments, the natural earth and manufactured transparent iron oxides, the extensive range of yellows, blues, greens, reds, and violets, Naples Yellow Deep (Chrome Antimony Titanate, a.k.a. Titanium Orange) and Nickel Yellow (Nickel Titanate). (Naples Yellow Deep and Nickel Yellow can both lighten and warm a paint mix, without casting a blue tint.) However, a few of his go-to inpainting pigments are missing from the product line.

Bernstein suggests making Zirconium Silicate (a.k.a. Kremer White), Raw Umber Greenish (Germany – Kremer #40630), Raw Umber Greenish Dark (Italy – Kremer #40612), and Vine Black paints from dry pigments and the QoR Watercolor Medium. Zirconium Silicate is a muted, translucent, controllable white, with low tinting strength, and a similar RI (1.93) to Lead White (RI=1.94) (CAMEO 2022c; Standford Advanced Materials 2024). These qualities make it an excellent alternative to the highly opaque and cool Titanium White, which can quickly deaden color intensity. Used leanly, Zirconium Silicate can also act as a matting agent to reduce gloss. Many pigments used for inpainting, including most earth pigments, are biased towards yellow, orange, red, and brown tones. The Greenish Raw Umbers, by contrast, retain a neutral bias when mixed with lighter pigments, making them invaluable options to other earth pigments. True Vine Black has large, splinter-like particles that stay separate and have low tinting strength when compared with other carbon blacks, which absorb considerable light and have powerful tinting strength and coverage. Vine Black is a gentle, controllable black that can be used to introduce traces of black to a color mixture without deadening it, as often happens when other carbon blacks are added to mixtures.

QoR paints can be tweaked with dry pigments and, if needed, more medium. In fact, Bernstein often prefers to use Vine Black dry pigments this way, as the unground particles are larger and more distinctive. To help simulate the sheen of an acrylic emulsion paint film, the tiniest amount of mica pigments can be added to an inpainting mixture. This tip comes from the workshop “Masterclass: Retouching Modern and Contemporary Paintings,” taught by Rachel Barker, a freelance paintings conservator based in the United Kingdom. Bernstein finds QoR Synthetic Ox Gall helpful for adding dry pigments to tube paints and for making new paints from dry pigments and QoR Watercolor Medium, as it reduces surface tension, improves pigment wetting, and enhances paint flow. Natural ox gall should be avoided; it has a highly acidic pH that can negatively affect some pigments, media, and supports over time (PMG Inpainting 2020). Glass mullers should be used to both grind pigments and to uniformly disperse them in the medium.

Diluent

QoR’s Aquazol binder, in addition to water-solubility, has an affinity for alcohols/acetone. The different solvents impart widely varying properties on the product, and this quality gives it a versatility advantage over other inpainting systems. Becca Pollak, a paper conservator at the Morgan Library & Museum who has assisted Bernstein in workshops, describes how leveling and the resultant gloss/sheen can be manipulated by the amount of water or alcohol/acetone used in diluent mixtures. The slow evaporation of a neat water diluent allows the paint to level, creating a more reflective or glossy surface. Conversely, a faster evaporating diluent, made using alcohols/acetone, produces a more matte paint surface by disrupting the leveling process.

Bernstein finds that a neat water diluent often evaporates too slowly for his applications and, consequently, makes inpainting difficult to control. If an inpainting paint is too wet, flooding, bleeding, and “picking up” can easily occur. Furthermore, it can take 3-5 minutes for inpainting to completely dry and exhibit its final appearance. Bernstein explains that including alcohols/acetone in a water-based diluent lowers viscosity, improves flow, and reduces the surface tension of QoR paints, in addition to speeding the diluent’s evaporation. The added alcohols/acetone can also reduce “pickup” of lower inpainting layers. Bernstein’s preferred diluent for QoR is a mixture he calls “Water-Zol” (Table 1).

Table 1. The recipe for “Water-Zol,” Bernstein’s preferred diluent mixture for QoR. 

This table gives a general recipe that can be tailored to the specific artwork being inpainted, as well as the ambient environment. The use of solvents, in particular benzyl alcohol, on modern paint surfaces should be monitored and tested closely for sensitizing, or otherwise detrimental, effects. If there is concern, components of Water-Zol can be left out. Likewise, if an object’s surface is water-sensitive, then alcohol/acetone alone can be used. Bernstein advises making new diluent batches each day of inpainting to keep mixture proportions consistent and clean from pigment and medium contamination. While inpainting, bottles of 2-propanol and acetone should be kept on hand to adjust the diluent, using a pipette, as needed.

Pollak typically uses QoR to inpaint screenprints and photographs (over an isolating layer) where very little medium can be put into a lacuna or over a scuffmark. By adjusting her diluent, she can make inpaints that are minimally bodied, like a traditional watercolor paint, but are well-bound and have the desired plasticity.

Kelsey Marino, a first-year conservation student in the SUNY Buffalo program, pointed out that QoR’s manipulatable finish can be helpful when inpainting non-Western paintings with matte surfaces, such as thangkas. Marino used QoR on a Thai painting that had a chalky-matte surface. She used acetone as the diluent because the paint was sensitive to other solvents, and it had the added benefit of making the QoR appear matte. She noted that, if too much gloss had developed from building-up inpainting layers, applying some neat acetone with a brush would bring back the matte finish. Using acetone had the drawback of causing the QoR to dry almost immediately, and, consequently, Marino had to hold her palette very close to the painting’s surface.

More Tips!

Beth Nunan, the owner and lead conservator at Flux Art Conservation, a private studio in Philadelphia specializing in the conservation of contemporary paintings, uses QoR with some frequency in her practice. However, before QoR was commercially available, she mixed tube gouache paints with Aquazol 200 and 500 (about 10-20% w/v solutions in deionized water-alcohol blends) to give her gouache paints more transparency and luminosity. By adding a final layer of Aquazol 200 over her gouache-Aquazol mixes she was able to mimic the surface sheen of acrylic emulsion paint. Nunan added alcohol into her solutions to help navigate Aquazol’s “stickiness,” although keep it at a minimum to protect the acrylic emulsion paint surfaces. Bernstein sometimes adds small amounts of Aquazol 200 to his QoR paint mixes, which increases the glass transition temperature of the product, making a stiffer paint with less tack. This addition also reduces the speed of QoR’s solubilization, which helps control pick-up.

If inpainting is needed directly onto a porous, absorbent substrate, such as paper, unsized canvas, or acrylic emulsion paint, a barrier layer should be applied before inpainting. This is important, both practically and ethically, to prevent any inpainting media/pigments from staining the substrate and to aid in its removability. Bernstein uses methylcellulose (Methocel A4C [3.2% w/v in deionized water] and Methocel A15C [2.7% w/v in deionized water], mixed in a 5:1 ratio) as a barrier. He prepares this mixture as a viscous stock solution and dilutes it as appropriate for the particular surface being isolated. Pollak prefers using JunFunori (1.0-2.0% w/v in deionized water) as a barrier on paper, although she also uses methylcellulose and Klucel G (≤ 1% w/v in alcohol), the latter specifically for water sensitive surfaces. Anne Schmid, a paintings conservator at the Stedelijk Museum Amsterdam, used two layers of Funori (1.5% w/v in deionized water) as her QoR barrier for a Rothko painting she conserved while working at the Menil Collection in Houston (Schmid 2022). She typically would have used JunFunori, but it was not available to her at the time. For this treatment, Schmid used deionized water as the diluent for her QoR inpainting due to the paint film’s sensitivity.

QoR can be used as part of a layered inpainting system, in which fills are first toned with watercolor or gouache paints, and QoR is then applied to match the final color, transparency, and gloss of the surrounding paint surface. Similarly, QoR can be applied as the lower fill-toning layer, and other resin-based inpainting systems, like Gamblin, could be applied on top. Due to its high RI, there is far less color shift when using QoR as a base for overlaying glazes, or when varnished, than gum arabic-based watercolor. Applying a brush varnish over QoR inpainting should be avoided, although, since it is relatively insoluble in aliphatic hydrocarbons, spray varnish applications should not affect inpainting.

Bernstein shared some final advice to aid any inpainting process, regardless of the medium. He recommends keeping color mixes as simple as possible and selecting a brush one size smaller than initially anticipated (i.e., go from a size “0” to “00”). Whenever possible, he positions an object vertically; to inpaint in this orientation, the brush is held upwards, which allows gravity to retain reserve paint in the belly of the brush and enables more precision with the tip. A compact hairdryer, used on low-heat or no-heat settings, can help speed the drying of aqueous inpainting. If appropriate, low-heat air can be used to desiccate a surface immediately prior to inpainting to preemptively limit bleeding and to speed up drying. Following inpainting, the hairdryer can be used again to set the inpaint and observe the dried color. Bernstein suggests that studios have a thermo-hygrograph that can be read easily across a room, as ambient temperature and relative humidity affect the handling and evaporation rate of aqueous media. He reiterated the need to be prepared to adjust diluent mixtures to suit the environment and project at hand.

—Fiona Rutka, Paintings Conservator, the Canadian Conservation Institute, fiona.rutka@pch.gc.ca; in collaboration with James Bernstein, Conservator of Paintings and Mixed Media, San Francisco, artdoc@jamesbernstein.com

Acknowledgements

We would like to thank the contributors, Ulysses Jackson, Kelsey Marino, Beth Nunan, Becca Pollak, and Anne Schmid, for generously sharing their knowledge and experience for this article; and Marie-Hélène Nadeau, of the Canadian Conservation Institute, for clarity reading.

References

Arslanoglu, Julie. 2004. “Aquazol as Used in Conservation Practice.” WAAC Newsletter 26 (1):10-15.

Berns, Roy, and René de la Rie. 2003. “The Effect of the Refractive Index of a Varnish on the Appearance of Oil Paintings.” Studies in Conservation 48 (4): 251-262.

CAMEO (Conservation and Art Materials Encyclopedia Online). 2022a. “Aquazol.” Museum of Fine Arts, Boston. Accessed July 30, 2023. https://cameo.mfa.org/wiki/Aquazol.

CAMEO (Conservation and Art Materials Encyclopedia Online). 2022b. “Gum Arabic.” Museum of Fine Arts, Boston. Accessed July 30, 2023. https://cameo.mfa.org/wiki/Gum_arabic.

CAMEO (Conservation and Art Materials Encyclopedia Online). 2022c. “Lead White.” Museum of Fine Arts, Boston. Accessed February 20, 2024. https://cameo.mfa.org/wiki/Lead_white.

Golden, Mark. 2014. “The Science Behind QoR.” Just Paint. Golden Artist Colors, Inc. Accessed July 20, 2023. https://justpaint.org/the-science-behind-qor/.

“Egg Tempera.” 2021. Painting Conservation Wiki. Accessed February 19, 2024. https://www.conservation-wiki.com/wiki/Inpainting:_Inpainting_Binders_and_Media#Egg_Tempera

Jackson, Ulysses. 2023. Personal communication. Formulator, Research and Development, Golden Artist Colors, Inc., New York.

“PMG Inpainting.” 2020. Painting Conservation Wiki. Accessed March 12, 2024. https://www.conservation-wiki.com/wiki/PMG_Inpainting.

Schmid, Anne. 2022. “Treatment of a Water Drip on Mark Rothko’s Untitled (1957) in the Menil Collection.” Paper presented at 50th AIC Annual Meeting, Los Angeles, California 2022.

Stanford Advanced Materials. n.d. “ZR2485 Zirconium Silicate Powder (ZrSiO4 Powder).” Accessed February 20, 2024. https://www.samaterials.com/zirconium-compounds/2485-zirconium-silicate-powder.html#:~:text=Zirconium%20Silicate%20Powder%20is%20a,1.93%2D2.01%20and%20chemical%20stability.

Further Information

Golden will work with conservators to develop bespoke paints (including in the QoR formula) for special inpainting projects: https://goldenartistcolors.com/contact-us?dept=customlab.

Large, hand-painted color swatch binders of QoR are available from Golden: https://shop.goldenartistcolors.com/qor-hand-painted-binder-chart-m730120.html.

Kremer Pigments offer small sized glass mullers (diameters = 4-6 cm), for grinding small batches of pigments in medium: https://shop.kremerpigments.com/us/shop/accessories/mortars-pestles-glass-mullers/.

Mastering Inpainting Workshops: www.jamesbernstein.com/James_Bernstein_Website/Conservation_Workshops.html.

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