This is what Golden wrote me in respond to my question regarding clear medium for acrylics.
Thank you for your email. We have several mediums that could be used for this purpose. The Gloss Glazing liquid is thinner than the Heavy Body Acrylics and can be added in any amount to acrylic paints. It has some retarder to slow down drying. It will increase flow and transparency. It can add up to an additional 15 minutes of open time depending on how much is added and the environmental conditions. The Gloss Glazing Liquid is roughly the consistency of house paint. For longer working time, the OPEN Medium can be used. The OPEN Medium has a similar consistency to the Glazing Liquid, but stays open for up to an hour or more depending. It will also increase transparency. Finally, retarder can be added up to 20% to the acrylic paints and mediums to increase the working time. At its highest ratio, Retarder provides an additional 15-20 minutes but doesn’t change the transparency or consistency as much as the other products. Reducing the absorbency of your ground can help paints stay wet longer. Increasing the humidity in the studio can also help. All water-based acrylic products are milky in the wet state. Unfortunately, that is the nature of the product and something acrylic painters have to contend with.
Here is an article about increasing working time with slow drying mediums: http://www.justpaint.org/open-mixed-...-time-control/
Here is product information on Glazing Liquid: https://www.goldenpaints.com/technicalinfo_glazeliq
Here is information on OPEN Medium: https://www.goldenpaints.com/technicalinfo_openmeds
We hope this information is helpful. Please contact us again with any additional questions or comments.
Materials Application Specialist
607-847-6154 / 800-959-6543