I recently did a test where I used a test swatch which consisted of normal thickness brushstroke of student grade acrylic (no added mediums or retarders). This has been left to dry for at least 3 months. I then brushed onto the very dried surface some normal cool tap water and let it absorb/evaporate over 3 days.
After this when I checked the test swatch I noticed that at the edge of the water affected area the surface of the paint was now more shiny than before (more of a gloss finish compared to the satin previously). It’s a bit like the water ring you get on paper how it alters the lock of the paper.
My question is what is happening here? Has the acrylic paint film expanded slightly with the water and has settled back in a slightly smoother layer (thus affecting the sheen). If not this then do you know why the tap water is affecting the acrylic paint film like this? And if it has any implications for conservation / using water with acrylic on multiple layers?
Thanks,
Richard Phipps
Thank you Mirjam! That is really helpful and interesting. I didn’t realise it would absorb the water as much as it does.
The swelling of acrylic paint films is a well-known problem in painting conservation and a typical challenge when cleaning acrylic paintings. Swelling can redistribute or extract mobile components (such as surfactants or thickeners) from within the paint film, which likely contributed to the glossy halo you observed.
How much acrylic paint films swell when in contact with water, depends on a number of factors, including paint brand or formulation and the pH and conductivity of the water solution. Alkaline solutions cause more swelling in general and the younger the paint film, the more readily it swells. Student grade acrylic paints with greater filler and lower binder content might also be more prone to swelling. Conservators generally try to adapt the pH and the conductivity of their aqueous cleaning solutions to the surface pH & conductivity of the paint film, to minimize swelling, if wet cleaning must be done. Here is an article that explores the topic in more depth: https://www.researchgate.net/publication/315112486_A_preliminary_study_into_the_swelling_behaviour_of_artist s’_acrylic_emulsion_paint_films
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