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Controlling Acrylic Painting Time Through The Use of Mediums

All the GOLDEN Paint lines mix readily together to adjust working times.

The key to controlling working time in acrylics lies in the ability to control the rate of evaporation of water. Once most of the water is gone, so is the ability to manipulate the paint layer. Therefore, in order to control acrylics one must control the water. This becomes increasingly important to be able to move from fast drying paint mixtures to slower drying paints as needed. Fast drying layers work well in the early stages of a painting to be able to block in color sections, and then gradually slow down the drying rate when blending and color gradation is required.

GOLDEN produces both fast drying paint lines such as Heavy Body and Fluid Acrylics, and the very slow-drying OPEN Acrylics. These paints are inter mixable and one can control the working time this way. However, it seems unreasonable to ask artists to maintain a steady supply of two paint lines, so the more realistic approach is to start with one paint line and modify it with a series of mediums.

Before we get into the mediums, let’s address the other key factors that alter painting time.

Factors Influencing Working Time:

  • Painting Surface Absorbency – Absorbent surfaces rob the paint of water and retarder, so well-sealed surfaces increase painting time.
  • Humidity – When there is more water in the studio atmosphere, the water in the paint evaporates more slowly. Arid climates are known to wick both water and retarder out of the paint.
  • Air Movement – Wind, fans, central air systems, even people walking by can help pull water out of the paint.
  • Temperature – Although temperature is often thought of as a main drying factor, it’s not as important as others, such as humidity and air flow.
  • Paint Layer Thickness – Thin paint layers are going to dry faster than thicker ones due to drying uniformly. OPEN additions greatly reduce skinning over.

The above factors cannot always be precisely controlled while painting, but being aware of them while painting and afterwards can make a big difference in working time and how long you’ll need to wait for paint to dry.

The Trick is in the Mix

While the OPEN products allow for a much more leisurely pace while painting, using only these paints means you have to wait much longer for each paint layer to dry before proceeding, similar to working in oils. Thankfully, OPEN is completely compatible with the rest of the GOLDEN staple of products! This offers the ability to adjust and dial in the amount of time you need to apply each brush stroke.

The “finger-swipe” test is used to test the working time of paints.

 

A Paint Schedule to Maximize Drying Times

“Paint schedule” refers to the process used for commercial applications like wood stains and car finishes. Here’s a schedule that gradually provides increased working time, yet provides underlying layers to dry quickly:

  1. Use a medium to seal the surface absorbency. For example, gessoed canvas is fairly absorbent. Use Fluid Matte Medium over the entire painting.
  2. Continue using Fluid Matte Medium with some paint to begin composition. Block in areas with a base color for the main parts of the painting. You can use other mediums too!
  3. Swap Fluid Matte Medium with Glazing Liquid as more details are further developed. Glazing Liquid improves the working time to about 10-15 minutes on the sealed surface.
  4. As more blending time is required, gradually include a little OPEN Medium into the paint mixtures. Increasing OPEN Medium mirrors the improved painting time, but the paints still set up and can be painted over relatively quickly.
  5. Completely replace Glazing Liquid with OPEN Medium. When the majority of the mixture is OPEN Medium (more than half), working time improves to 45 minutes to an hour. Longer drying time before repainting is now required.
  6. Replace standard paints with OPEN Acrylics. As a system, OPEN products increase working time to an hour plus, and remain working for many hours more. Waiting until the final stages to convert allows for all of the subtle details  that make the painting complete.

Using fast drying products in the beginning stages allow for a rapid buildup of both color and medium, both serving to seal the absorbency more than thin color washes on gesso. In turn, this foundation provides more blending time as details continue to be added in. Even if you wish to start off creating soft edges, shadows, and color blends, be sure to seal the surface with Fluid Matte Medium or a gloss medium/gel if the glare isn’t too distracting for you.

Note: Jumping around between mediums while painting is possible, but realize that any slow-drying layers will take longer to dry before you can paint over them without lifting partially cured paint layers.

The below table gives a good guideline for general timelines for what kind of working time you’ll have when working on a semi-absorbent and a sealed surface.

Table 1 – Various base mediums tinted with Heavy Body acrylics are tested for working time on gessoed Mylar and a lacquer-sealed Paper Stock. Temperature was 70 degrees F, Relative Humidity was 58%

Blending Standard Acrylics with OPEN Acrylics

Although the presented painting schedule highlighted the use of mediums to adjust working time, the specific products used are up to each artist. For example, if you already own a fair amount of GOLDEN Heavy Body Acrylics, use them with the various mediums. The same goes for GOLDEN Fluid Acrylics or even GOLDEN High Flow Acrylics. There’s no need to also get a set of OPEN Acrylics if the required working times are being met. However, if the longest possible working times are more critical for your painting style, then OPEN Acrylics modified with OPEN Medium, OPEN Thinner or Glazing Liquid are the better option. The key takeaway is that all of these products are completely compatible.

Further Reading:

http://www.justpaint.org/extending-the-acrylic-range-developing-open-acrylics/

https://www.goldenpaints.com/technicalinfo_openmeds

https://www.goldenpaints.com/technicalinfo_opendrytime

https://www.goldenpaints.com/technicalinfo_drying

http://www.justpaint.org/suggested-drying-times-between-acrylic-layers/

http://www.justpaint.org/understanding-and-controlling-acrylic-drying-time/

http://www.justpaint.org/investigating-the-drying-process-of-acrylic-color-and-gel-medium/

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4 Responses to Controlling Acrylic Painting Time Through The Use of Mediums

  1. Kristine Martens May 23, 2018 at 11:55 am #

    Thanks for this study. My adult students will appreciate the structured approach to to information.

    • Michael Townsend May 25, 2018 at 9:07 am #

      Thank you Kristine!
      – Michael Townsend

  2. Felipe vera June 18, 2018 at 2:02 pm #

    I’m going to paint a Buddha statue with acrylic pain. What’s the process I should use to prepare the statue, made out of plaster (which is a dark patina)

    • Michael Townsend June 18, 2018 at 3:28 pm #

      Hello Felipe.
      Thank you for contacting us with your questions.
      We have another Just Paint article that describes painting acrylics onto plaster, located here: http://www.justpaint.org/painting-plaster-with-acrylics/.
      Please review the article and get back to us if you have any additional questions.
      Regards,
      – Mike Townsend

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