MITRA Forum Question Details

What you re describing in terms of underpainting with gesso is very similar to pastiglia but without the gilding. I see no issue with it but you will find that it is more difficult to do than it sounds. You need to apply the glue-bound layer thinly and in multiple steps otherwise there will be cracking.

I see no advantage to tempera grassa other than that it is a little less matte and requires a little less of a sizing layer. You will definitely need to seal any gesso layers, including “gesso Impaste” before painting in oil.

Distemper is a term most accurately used to describe pigments bound in animal glue. Gesso is most accurately used to describe a ground containing gypsum bound in animal glue. Many use the term for other inert white fillers in animal glue and even, much to my chagrin, acrylic dispersion-bound grounds from white, to black, to colorless. When taken to this extreme, the term gesso has become meaningless, other than to indicate a ground rather than a paint.

I would love for Koo to Weigh in on this but in general, tempera grassa does not really allow for much more flexibility in handling over traditional egg yolk tempera. You can get away with a bit more robust impasto but cracking and powdering are a possibility. You need to test.

I would not isolate before painting in tempera grassa, it would be preferable to isolate before painting in oils. Glue is a possibility for an isolation coat, but it needs to be done carefully. Thin shellac is fine if you are covering the whole surface with oils and the coat is not too glossy. It does introduce an alcohol soluble layer. I have personally isolated with a very dilute alkyd medium as long as all surfaces will be covered with somewhat opaque oil paint. This seems like sacrilege, but in many ways is corresponds with transparent isolating coats used in the Renaissance. Again, testing should be done on sacrificial pieces.

Both traditional gesso and an egg/oil emulsion, if applied too thickly, are likely to crack because of how they dry - as the water content in a thick layer evaporates out, the layer quickly shrinks and ends up looking like a dessicated lake bed (i.e. with fissures; sometimes visible to the naked eye, sometimes visible only using a loop).  So you won't be able to build up much impasto with either gesso or tempera grassa in a single layer; perhaps up to about 1 /32" (.8 mm), or a hair more, for a single layer?  You might get away with 1 /16" (1.6 mm), but I could see that developing hairline cracks (you should check under a lens to be sure).  Some of the bodied acrylic paints can produce more pronounced impasto and dry more reliably.  Or, you could beef up oil paint will calcite for more impasto... but I think you're looking for a fast drying, water-based way to get impasto - if so, I'd say acylics are your best bet.  What do the Golden technicians say?

An interesting technique, I'd be curious to see the results.  I personally don't like painting with particles above about 30-40 microns, at most; larger than that and the paint is too gritty for me. So, 150+ microns is definitely outside my comfort zone. Setting aside personal preference, I'd also be concerned about adherence with such large particle sizes in TG (in a pure oil or acrylic binder, maybe yes - but not yolk); however I don't have any testing to back that up, it's just my two-cents worth.  

As for your layering, when you say "first glue size attop it", that "it" refers to the gesso, yes?  You're first sizing  gesso, not the TG, correct?  I just want to be sure I understand the layering correctly.  As Brian notes, sizing traditional gesso is necessary only with oil paints (true gesso is so absorbent it really soaks up too much oil binder).  With water-based paints (egg tempera and egg/oil TG) the absorbency of the gesso mostly takes up the water in the paint, and this, in fact, is helpful to controlling the paint.  So if you are working with a majority yolk, water-based tempera grassa paint (versus majority oil, solvent diluted TG), either don't size the gesso or do so minimally; water-based TG will bead up, not behave well if you apply too much size to the gesso.

And yes, I understand the passion for historic materials!  Acrylics are marvelous paints that can do many wonderful things, but natural binders are very compelling, for sure. 

Koo

​I worry about the extreme surface tension of an ASG isolating layer over fatty (or traditional) egg tempera layer. Animal glue is a massively more powerful adhesive, including great surface tension as compared to any tempera system. If it were me, I would use a thin, dilute oil (or preferably, sacrilege be damned) a very thin oil-alkyd coating, before oil painting. I really worry about pulling up the tempera with the ASG coating.

​​I agree with Brian - glue atop TG isn't a good idea.  

I've painted oil paints directly on top of TG, no isolator; there was a little sinking in, not too much, and after two or three layers the surface was saturated and oil paint went on fine.  If you first sized the gesso ground with a thin coat of glue, to decrease it's absorbency, that would likely further lessen the amount of oil sinking in atop the TG.  Or, as Brian suggested, you could isolate it with oil, or oil+alkyd; I've done the later using approximately 1 part alkyd to 8 parts oil, and the alkyd really helps the oil layer to dry more quickly. 

In addition to adherance and shrinking questions, I'm concerned that if you isolate the TG it won't cure very well.  No coating is impervious, so oxygen would still reach the TG layers to encourage polymerization - but it might slow things down, or create uneven drying rates. Brian, what do you think of that - an issue, or not?

So, I think I'd go with...

1.  Traditional Gesso

2.  Optional: Thin Glue Size

3. Tempera Grassa

4.  Optional:

Transition to increasingly more oil based, solvent-diluted TG

or

Apply a thin oil + alkyd layer

5. Oil Paint

​As for particle size, in fact I don't much enjoy above 20 microns, and am happiest in the 1-10 range, but that's just me.  I've gone as high as 100 microns (with dioptasio) and it looked/felt like rough grit sandpaper. The 30-40 micron number I suggested was just a rough guesstimate as to what size particle a yolk binder can effectively handle.  

Koo