MITRA Forum Question Details

ApproveRejectUn-ApproveThe other half of this question that warrants info relates to reworking an already dry or partially dry or touch dry painting :J

ApproveRejectUn-ApproveI will quote the relevant sections of the "Varnishes" document (found in the Resources section) here:

Make sure that your painting is free of surface grime and dust before continuing to work. A lint-free cloth and/or a soft bristle brush can be used to clean the surface

It is particularly important to avoid applying moderate to thick layers of retouching varnishes or layers of oil during the painting process as this could lead to potential delamination and/or cracking of the paint. As most varnishes remain sensitive to solvents, varnishes should not be used as the primary paint medium or applied in between paint layers. Paint applied over a varnish layer or mixed with certain amounts of varnish can remain sensitive/soluble should the artwork require future conservation treatments.

For oiling out during the painting process or for cutting the absorbency of a ground artists are recommended to 1) apply a thin layer of oil locally as needed or globally (consider using stand oil/thickened oil thinned in a solvent if your paint/ground layers are extremely absorbent) to matte/sunken-in areas 2) remove any excessive oil using a lint-free cloth and 3) wait until the surface is dry to the touch.

If the surface of your painting is fairly “fat” already (e.g. sufficiently bound with oil binder) then you may end up dealing with adhesion problems, either immediately or later down the road. In keeping the “fat over lean” principle in mind, the surface of the paint may require a bit of gentle roughing up in some instances (either locally or globally) to ensure that subsequent paint layers sucessful adhere. This can be done with extremely fine grit sandpaper, followed by an overall “rinse” with mineral spirits or OMS. If the paint is only touch dry, it may still remain soft beneath the surface in which case sanding would not be advisable. Kristin deGhetaldi

ApproveRejectUn-ApproveThe safest to the paint already applied, as well as to the overall structural integrity of the painting would be to oil out very thinly with linseed or walnut oil, with no solvent, and only on the area to be painted into in the immediate session, and perhaps slightly beyond that area. After the oiling-out oil has been brushed on thinly, lay a paper towel over it, holding it in position with one hand while rubbing over the towel with the other hand, the objective being to blot as much of the oil off as possible. Just enough will remain on the surface to re-saturate the dried colors and lubricate the surface so the new wet paint will glide on seamlessly. The tiny amount of oil involved will become incorporated into the new paint and/or will be absorbed into the dried paint below, and thus will essentially disappear by the time the painting is finished. This is preferable to using retouch varnish for this purpose, because retouch varnish could (and probably would) interfere with adhesion between the layers of oil paint, and the presence of a soft resin in a paint layer renders it more susceptible to solvents normally used in removing old varnish in restoration procedures. This means the likelihood of some of your paint coming off when the varnish is removed is greater if you use retouch varnish while painting, or if you add a soft resin to your paint.

ApproveRejectUn-ApproveI think the last comment (11-23) needs qualifying about its claims for structural accuracy. Is it not important that the underpainting is either fresh ie still wet or fully dry (not recently touch dry) before painting over and that the surface is slightly rough (rough it up eg with a cuttlefish or sandpaper if it's not and don't breathe the dust or get it on you) or matte- satin at most. Oiling out an old painting before painting into the oil couche doesn't aid structural integrity (it's used to stop sinking in or if you want to paint to glide on or for a visual aid especially to match tones). If you need to add oil to the paint (fat over lean general guide) because you added oil to the previous layers, then add oil to paint, don't oil in. Walnut oil doesn't help structural integrity, it forms weak bonds

ApproveRejectUn-Approveaddition to my last comment about walnut oil - it's sometimes used in final layers as it's slower drying (& marginally less yellowing than linseed) but differences in drying time between different drying oils seems to level out after 3-4 weeks and linseed oil is apparently fairly stable after a month (in terms of weight gain & loss). So for a painting 3 months old using walnut oil won't help much. Resident experts please correct this if it's wrong