Genesis heat set paints and the world of polymer clay

I did 20 or so paintings with Genesis heat set paints several years ago. They offer some compelling advantages. These really are not gimmicks!

  • Paint stays open indefinitely until heat set.
  • Indirect techniques and multiple glazes are possible without long waiting periods.
  • Mediums dry without yellowing, at least in the years I have had my paintings. As with acrylics, mediums can be used for translucent effects that would have oil painters wallowing in problems with linseed oil yellowing.
  • Brushes can be set aside for days without cleaning. You can really just walk away from your painting and come back to it days later. The biggest problem is that paint mixes last so long that they can gather dust.
  • Genesis can match oil paint for color density, especially compared to paints like Golden Open and Atelier Interactive, which are often portrayed as oil substitutes.

But, Genesis also has distressing disadvantages:

  • A very narrow range of mediums with very limited behavior, and no way to overcome the ever-present thixotropy without weakening the paint.
  • Tendency to thicken dramatically on the palette and canvas over time (that’s thixotropy).
  • A small range of surfaces that the paint is reliably compatible with, unless you gesso it yourself. Many acrylic-pre-primed surfaces are too absorbent and suck the plasticizer out of the paint. I believe the plasticizer can even soften some acrylic gessos, which can border on disastrous. I find Fredrix gesso (and Fredrix pre-primed canvas) the best for a smooth, slick feel, and Golden gesso is useful for more brush drag.  Amaco also recommends Pro Art gesso.
  • Difficulties with heating arrangements, especially with large canvases. Only ovens are really sound, in my opinion; the heat gun is too hard to use long enough and evenly.  I invested a fair amount of money in the Genesis oven, and can still only go to 24 x 24 inches. If you don’t want to buy that, make your own heat box, or use your kitchen oven (I sure wouldn’t do that), you will be limited to small sizes up to 12″ x 12″ that fit in a convection oven.

I eventually set them aside, but I recently pulled them out and did a few more paintings. The  problems remain (even with new thick medium and a few new colors that I bought to see if they have changed anything), but I stumbled upon some intriguing possibilities of combining them with products from the polymer clay world.

I’ll insert here that I’m happy to communicate with anyone about these paints, but I had to close comments because of spam. If you want to reach me, I’m on g mail using the name jaymacazbd.

Both Genesis and the polymer clays are plastisols, mixtures of PVC with a softening plasticizer that keeps the product workable until heat is applied. Plastisols are widely used in screen printing and other industrial applications, with new products under development, and the polymer clay vendors seem to be taking advantage of this more than Genesis.   In particular, all three major lines of polymer clay (Sculpey, Fimo, Kato) offer so-called liquid clay, which appears to be very similar to the clear Plastisol bases used in silk-screen printing. In spite of the “liquid clay” name, these mostly do not have any clay ingredients, so I’ll call them polymer heat-set mediums.  They turn out to be quite useful.

These liquids can be mixed with pigments to create paint,  used as adhesives, mixed into clay to soften it, or combined with Genesis paint. They are heat cured at temperatures similar to Genesis. So far, they appear to be more reliable for heat-curing than Genesis, which is a bit prone to sticky patches and uneven setting, at least with a heat gun. If added to Genesis, they seem to confer their improved heat-setting to it.

They also extend the rheology (paint behavior) considerably, with the possibility of long, honey-like strands (like clear tar gel in acrylic); or ropy, taffy-like strings (like sun oil).   Polymer clays can even be softened and mixed into the mediums for textures. Unlike Genesis, most of the polymer clay mediums have complex dilatant rheology — the cornstarch effect of getting stiffer the harder you agitate them, then melting when left alone or moved gently. This is the opposite of Genesis thixotropy, so they combine for a surprisingly wide range of behaviors. With added pigments, most of the clay mediums are quite long, pulling into strands easily, while Genesis is short.

I contacted Amaco (the maker of Genesis) and asked about compatability with Genesis paint. They saw no problem with combining these mediums with Genesis as long as the temperature range is compatible.

I have tested Genesis mixed with Sculpey Translucent Liquid (TLS) and Sculpey clear liquid, Sculpey Bake and Bond, Fimo Liquid Decorating Gel, Kato liquid, and Kato paste.  They each have pros and cons. No single product is perfect for everything, but it appears they can be intermixed to make custom mediums.

  • TLS is a good all-around medium that seems very strong after heat setting, but it is the whitest of them all before heat-setting. Since it gets more transparent after heating, this causes moderate color shift; after setting, paint is a little darker and has a matte finish. TLS can be mixed with Sculpey clay softener at about 6:4 for a good thinning medium for Genesis, without much color shift.  This mix will fully heat-set by itself, so it can be safely added to Genesis in any proportion.  For more gloss, some Fimo can be mixed in (or maybe the new Sculpey Clear).  TLS can also be mixed directly with pigments or calcium carbonate to make some very nice texturing mediums.
  • Sculpey Clear – this came out in 2017. My initial tests are that it isn’t a great paint medium for me. Mixed with pigments, it tends to have broken and rough edges. Kato paste and TLS are both much more charismatic paint mediums. However it is very transparent and more glossy than TLS, especially if a final heating with the heat gun is done. Sculpey warns that it can yellow with repeated bakings, recommending no more than 30 minutes total at 300, which may make it less than desirable in earlier layers. I haven’t done careful tests on this, so I don’t know what to expect. It’s possible that baked at 265 degrees instead of 300 degrees, you may be able to take it through many more baking cycles. I have not yet seen any yellowing.
  • TLS Bake and Bond doesn’t look good to me so far. When mixed with Genesis, I have noticed tiny bubbles in the paint film after drying so I’m off it for now.  I will try it as a glue to mount canvas (I’ve been thinking about testing out heat-set canvas mounting), but I’m not using it as a paint medium.
  • Fimo  is completely clear before heating, so has no color shift issues. It dries with a nice satin/gloss sheen. It is stickier than TLS, like honey, and feels the weakest (most dentable) after curing.  It sets at the lowest temperature, which probably affects its strength. Still, the clarity is great.
  • Kato paste is very nice for texturing. Add some pigment or Genesis and you can pull out long taffy-like strings that are very charismatic. Dry pigments are useful to adjust consistency because it tends toward melting. So far it seems very strong.  I have made something a lot like Kato paste by mixing Kato translucent clay with Kato liquid.
  • Kato liquid is thinner, and is the most dilatant of the mediums, which is fun for some effects but not always desirable.  Even a small amount of Kato liquid added to Genesis paints will overcome thixotropy and cause melting. This helps with thin applications but puts you on a knife edge with impasto: too much and your marks melt within minutes.  Both Kato mediums should be heated at the high end of the temperature range for Genesis, or heated for longer. They are whitish before heat-setting, so cause a slight color shift. They dry quite clear and glossy in thin coats.  Unfortunately for me, I find something about the smell of liquid Kato kind of difficult. I need good ventilation to work with it.
  • Kato makes a line of liquid colors; I have tried the opaque black and white and find they have strong dilatant rheology like the clear medium.   They are very liquid and melting, so not much use as paints without adjustment, and the colors dry much more transparent than their wet state. No info is available on the pigment color index numbers, which is not really acceptable to me, but most likely the blues and greens are phthalos and should be fine. Overall, I don’t find they offer any real advantage over the clear medium for painting.
  • Update: after several paintings, I am learning some precautions to take when I use polymer clay mediums in a dense texturing paste. If it’s made too lean and allowed to sit too long on canvas before setting, the plasticizer seems to leach into the ground and leave poorly bound paint, causing adhesion problems.  This seems to be highly time dependent. I have also seen some problems with bubbles in the surface of paint, which in a worst-case scenario have resulted in complete lifting of the texture off the gessoed ground.  Ouch!  After a few incidents, I noticed a pattern: this happened on some surfaces when the texture was heat-set, then overpainted fairly thickly and left without heat-setting overnight or longer.   It’s noticeable that the wet paint loses its gloss, so I think the plasticizer is soaking into the heat-set texture, finally breaking its bond with the gesso if adhesion was poor to begin with.  I have tested this on different gessoed surfaces.  Grounds that performed badly are Fredrix gesso (which works great with Genesis alone), Golden absorbent gesso, Liquitex white and clear gessos, and Golden matte medium.  Grumbacher and Golden regular gesso did very well as long as the texture was set pretty quickly.  (Grumbacher shows signs of being one of those gessos that can be softened by plastisols over time.)  Why does this happen with the polymer clay mediums but not Genesis paint?  I’m guessing the dilatant quality of the mediums may be at fault. Dilatant mediums have a sort of self-adhesive quality that may be stressing the bond to gesso.  So my thoughts on this are:
    • Use one of the toothier gessos to get a good mechanical bond to the texture, and heat-set it quickly before the plasticizer begins to leach, or
    • Heat-set upper paint layers frequently, and don’t leave them wet overnight, or
    • Start the painting with Genesis and leave texture to later layers.

It takes a while to figure out what’s working. I’ll update when I know more.

It is possible to make heat-set paints directly using the polymer mediums and dry pigments.  The biggest problem with making paints with the mediums is that they are marketed to crafters in ridiculously small bottles! Sculpey TLS is only available in 2 oz. bottles, and I had to order Fimo from Europe to get a decent price and bottles larger than two ounces. The best prices I have found so far in the U.S. are at Munrocrafts.com using their 50% off of $200, but that’s a lot of 2-ounce bottles!  (If you get on their mailing list, you’ll be notified of half-off days that don’t require such a large purchase.) I have made paint directly with TLS. Kato, and Fimo, and they all worked well. I usually go for the convenience of Genesis, though, so combine the polymer mediums with that unless I’m after a specific effect.

Temperature issues

One question that arises is how to deal with the different temperature ranges of the mediums if intermixed.

  • Fimo – 230 to 265 F
  • TLS – 275 F
  • Kato – 275 to 325 F
  • Genesis – 250 to 280 F

So far I haven’t had any problems that I have noticed, and polymer clay artists seem to mix products pretty freely.  From what I know of plastisols, it’s reasonable that they should receive an averaged temperature based on proportions of different mediums, but polymer artists differ in their recommendations.  In practice, 265-270 degrees F has worked well for me using Fimo and TLS, and even Kato if drying time is extended. Amaco suggested only using 40% Kato to 60% Genesis, and heating no higher than 280 F.  They warned that some artist supports can begin to smoke above this.  I haven’t had any problems so far with adding more Kato than 40%, in fact I’ve done some texture layers that are almost pure Kato.

Update: I have had one problem where a medium clearly darkened/burned. At first I thought it was Fimo heated too high, but I think it was more likely caused by putting a painting into a convection oven without pre-heating.  The pre-heating cycle puts the heating elements on too high.  Always pre-heat!

One really useful thing I have learned from the polymer clay artists is to be much more careful about heating than Genesis literature would indicate.  Genesis markets a heat gun as a primary curing method, but it has always been troublesome for me, leaving patchy areas that don’t set fully. (White is particularly prone to this).  Polymer artists are very careful about maintaining consistent heat, and recommend longer heating times in an oven.  Based on advice, I have bought a small convection oven for about $90, and have had good results with it so far (for paintings up to about 10″ x 12″).  I have also begun to place a layer of papers or cardboard under the canvas to even out the heat.  It is really useful to be able to call on the experience of the polymer clay artists! Their advice has made me much more confident about getting good heating results with Genesis.

The polymer mediums generally call for heating 10-30 minutes in an oven, and some artists recommend as long as an hour. I think the very long times are for thick objects, beads, and sculptures. With paintings, my experience is that a heat gun can be used as a temporary solution for thin layers, but both Genesis and the polymer mediums should have a final cure in an oven for at least 15-20 minutes.  One bit of science I found is that plastistols cured at the lower edge of their temperature range should be cured much longer to compensate. One site claimed that a 10 degree Fahrenheit difference requires heating for twice as long.  In practice, I have found that a 1/8″ thick Kato texture mix sets well at about 265-270 degrees F for 20 minutes.

All in all, these new mediums have made painting with Genesis much more interesting to me, and opened some intriguing possibilities of combining paint with clays for textural and sculptural effects.

Postscript about plastisol: Delving further into plastisol science, I spent some time looking at info about clear plastisol bases used in silk screening.  Plastisols for silk screening generally cure at 325 F, and can be flash-cured, ie the paint layer only has to reach this temperature for a short time, the same as Genesis.  Polyester and some other fabrics can’t be subjected to that heat, so low-cure additives are available to bring the curing temperature down below 300 F.  These additives bring some problems with them: sticky spots if the heat is too high or applied too long, tendency to get viscous when they sit around.  These are very good descriptions of problems with Genesis when a heat gun is used.  I suspect they decided to use the additives in order to get a curing temperature of 265 F, achievable with craft-level heat guns and safer for artist canvas and stretchers.   It seems likely that the polymer mediums are also using these additives, since all of them say they will cure below 325 F, and yet they seem to cure better than Genesis.  Perhaps plastisols have improved and these mediums benefit from that.