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Why your Oils Don't Dry

I'm just prepping for my studiotalk tomorrow, and as we're heading towards the end of Season 1, it seemed a good time to recap on the studies I've done with you, and see if we can't inject a bit of extra quality into them. Accordingly, I'll be covering a bit of studio craft so this article from my 2014 archive came to mind. It's a primer on making your oils dry that bit faster, ideal if you want to get around to working them up in a more timely manner.

Oil Painting Problem Solver


Norfolk painting school modern resin and solvent

Drying and Varnishing


Few aspects of oil painting are shrouded in as much myth as drying and varnishing oils. To answer this one has to understand how oils dry, and why they need varnishing at all.


Efficient Drying


The slow drying rate of incorrectly handled oils can be a huge disincentive to taking them up. For this reason one of the key skills I teach in studio craft is getting them to dry in a reasonable time. When correctly applied oils can be workably dry within an hour or so and soundly dry in a couple of days.


By workably dry I mean the oils can be overpainted whilst retaining a purity of colour (and avoiding the dreaded ‘grey mud’ familiar to most new painters!). Soundly dry oils can be overglazed without lifting them away from the support.


The key thing to remember is that oils dry not be evaporation, but oxidisation. Therefore pigments which are low in oil (are ‘lean’), or are full of natural driers (siccatives, such as metal salts or lead), and are applied thinly, will dry far more quickly than pigments which are not.


Painting very thickly, adding extra oil (such as a linseed medium) or working on an unabsorbent ground will all greatly retard the drying of oils and vice versa.


So for very rapid drying oil painters prefer to choose pigments which are lean, full of siccatives, work thinly and to do so on an absorbent ground. Here is a checklist of simple ways to make your oils dry more rapidly


  • Paint thinly

  • Use an absorbent ground such as a traditional chalk gesso

  • Use a siccative or resinous medium such as Galkyd

  • Choose naturally siccative oil colours or add them to your mixes (e.g. natural earth colours, Lead White etc)

  • Never add extra oil to your paints

  • Dilute your oils with a little solvent (but see below before you do this)

Sinking in


Many oils appear surprisingly dull and matte when they dry; a phenomenon called ‘sinking in’. Sinking in is caused when oils have an insufficient quantity of oil within them to dry with a characteristic lustre.


The most common cause of this is diluting oil paints with solvents, but it will also occur if oils are applied to an absorbent gesso creating ‘leaner oils’. Lean oils are actually a very good base for painting upon as they create a key for subsequent layers of oils to bind with, but are unattractive if found in the top layer of a painting, where they will appear as dull patches amongst passages finished with fatter oils.


If you paint a picture in traditional earth colours, then add a passage which is rich in Titanium White you’ll see this very clearly. The earth colours will dry very rapidly, to a matte finish than the white which will dry much more slowly but to a more lustrous sheen.

Oil painters traditionally avoid sinking in and regulate both drying rates and the lustre of their oils by using a medium, however it’s not possible to be certain one has an even sheen until the oil is absolutely dry. Here is a list of notably fast and slow drying oils.


Faster drying Oils

  • Lead White (Genuine PW1, not a Hue)

  • Raw Umber

  • Burnt Sienna

  • Raw Sienna

  • Yellow Ochre

  • Terre Vert

  • Prussian Blue

  • Manganese colours (i.e Manganese Violet)

  • Cobalt Colours (Violet, Blue, Teal etc)

Slower Drying Oils

  • Titanium White

  • Ivory Black

  • Arylides (i.e. Arylide Yellow)

  • Quinacridones (i.e Quinacridone Red)

  • Alizarin Crimson

Oil paint is capricious stuff; with each individual pigment determining how fast it will dry, and how lustrous it will appear when it does. Michael Harding has taken the trouble to print the drying rates of his paints on their labels and you could do far worse than take his colours as a starting point for your own work.


Varnishes






The role of varnishes in oil painting has changed enormously down the centuries. Originally intended to be nothing more than a washable top coat for tempera and oil paintings, varnishes became central to the painting process itself, before reverting in modern times to their original role.


It’s probably the changing roles of varnishes within the oil painting process which has led to the confused and contradictory information offered on when and how to use them.


The greatest advantage of a varnish is that it will create an optically unified surface, correcting all of that pesky sinking in, and deepening colours as well as protecting the painting surface while it does so.


The oldest type of varnish still available is Retouching Varnish. Originally intended as a weak and quick drying varnish to rapidly isolate and seal volatile pigments, retouching varnish has no real role in modern oil painting.


Most traditional varnishes are resin based - dammar or Copal for instance, and rapidly discolour with age, yellowing and darkening paintings (see above), and for this reason a true varnish should be absolutely removable - which is to say it should not crosslink or bind with the painting under it. For traditional resin based varnishes, which require storing solvents in their preparation, the potential to crosslink is high unless the painting under them is both technically sound and chemically dry. If one's process is erratic and rapid then varnishing is never going to be sound, in an archival sense.


Turner for instance worked with a cocktail of waxes, gums pigments and resins which would, in the best of technical situations, be difficult to varnish over, yet he did so in such a cavalier fashion, that one can only assume that knowing varnishing them to be so problematic as to be impossible, he simply strove for the look of the thing, and left conservation to look after itself! In Turner's defence, the very best way to put an ethereal shimmering ghost of a glaze over a passage is often within a top varnish - but the result we se today is isolated bleached out blogs of impasto floating on his work, stripped of their fine glazes by the clearing off of those varnishes.


Modern varnishes - such as Gamvar - offer everything traditional ones do, with one crucial difference. They are made with very mild solvents, offering very good resistance to crosslinking.


For a matte option one can always varnish with cold wax, its an incredibly safe option, but offers less depth of colour, albeit at a much improved viewing angle. The ideal choice for hanging work in raking light.



In a nutshell


Oils dry by oxidisation,

Calcites and short grounds leech oil, promoting faster drying

All oils sink in as they dry but this with Calcites and on short grounds sink in more.

Varnishes unify surfaces correcting sinking in

Retouch varnish is largely unnecessary with modern pigments

Traditional varnishes dry fast and glossy but tend to crosslink and yellow

Modern varnishes are the best choice

Opt for wax to improve viewing angles, but it doesn't deepen colours.

ENDS

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