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Archival Oils' Lean and Fat Mediums

When you first start painting with oils, one of the “rules” you hear about is to follow “fat over lean.” What does fat over lean mean anyway? It means that in order to properly develop an oil painting that will not crack, you should start with “lean” layers, using oil paint mixtures that typically are thinner with more solvent than medium and less flexible, followed by more “fat” layers, mixtures that have more medium than solvent, and are more flexible. The reason you need to follow these rules is because oil paints dry by oxidation, and subtly shift and move over time, causing cracking if you have a less flexible layer (lean) on top of a flexible layer (fat).

Happily, when you paint with Archival Oils and Odourless Lean and Fat Mediums, you don’t need to follow these rules because Archival Oils are the world’s only flexible oil painting system. That’s right, this flexibility is built right into the paint and mediums, so you can explore a whole new range of techniques and not worry that your painting will crack over time. It’s modern technology applied to the centuries old art of paintmaking!

Archival Lean and Fat Mediums have been specially designed for artists to give them ideal working properties. They are alkyd-based, which means that they tack-up and dry relatively quickly, in about a day or so, allowing you to build up your oil painting without waiting weeks for each layer to dry. These mediums also add a unique, natural translucency to the paint, and help Archival Oils flow in very desirable ways.

Lean Medium is used for thinner paint techniques. It is similar in consistency to a traditional turpentine+linseed oil mixture. But Lean Medium is based on isopar, not turpentine or mineral spirits, so it is odourless and releases fumes at a very slow rate, producing a much safer painting situation. Lean Medium dilutes Archival Oils for underpainting, glazing and all around liquid painting. NY Stream was created using Lean Medium throughout the piece – note the glaze on top of the heavier, more impasto rocks. If I had put such a thin lean glaze on an impasto area using conventional oils, I’d be setting myself up for disaster! .

Fat Medium is also used for thinner paint techniques, but is more syrupy. It would be similar to a linseed oil+ turpentine mixture and it feels oily. Like Lean Medium, Fat Medium is also based on isopar, and is odourless to minimize health hazards. Fat Medium increases gloss and sheen, and is wonderful for Flemish layering techniques, where darks are built up with rich transparent layers. Early Spring was created with Fat Medium – note the rich darks created by the glossy layers.

Both of these mediums can be mixed in any amount with Archival Oils, and added to each other to create your own custom solution. Try them once, and you too will fall under the spell of painting with Archival Oils!

There are (2) Comments, Comments are now closed for this discussion?
  1. comment_1_9951

    Jim Cobb commented on June 15, 2010, at 3:28 pm.

    Kerryn Madsen-Pietsch from Artropica Innisfail Studio Gallery sent us a query about preservation the of an old oil painting. See below details of the work and my answer.

    Kerryn writes,
    "I have cleaned away carefully the old varnish on an oil painting done on masonite, dated 1970. This was an award winning painting and consists of a semi-abstract opaque unique shadowy image with visible and variable brush size marks applied and paint colours overlayed sporadically in blocks of multiple 'low' muted earthy key colours. Thinner paint brush mark underlayer areas are still visible between top thicker layers.

    There is visible evidence that the gesso ground is not stable as whitepowdery film is showing up minimally throughout areas of the oil painting, as was also before the cleaning process.

    The paint is generally not brittle or cracking in any area, however it does has a dull and 'matt' tonal appearance but the oil paint is not powderyas happens when a surface has not been sealed/prepared at all appropriately for oil paint/binder adhesion.

    Would you please advise, as manufacturer of the Archival Flow Gel Medium (possibly thinned slightly with the Lean Medium for less body) if this product is recommended for use by itself, as a topical clear glaze binder. I am wanting to improve the sheen and enhance the colours. I am interested whether this aalkyd medium can act as a 'stabilizer' for the painting before applying a final matt finish?"

    Later Kerryn also mentioned that the gesso substrate appeared disturbed in a few fragile areas. i thought that this might be of wider interest so my response is posted below.

    Since I am unable to see the painting that you speak of, the response that I’m giving may not be completely precise.

    You mention an old oil painting where the gesso layer seems to be a little bit unstable, and of course since it is the gesso which is adhering to the canvas and it is underneath the paint on the painting you can’t do anything definitive to improve its adhesion. All you can hope to achieve is to freshen the painting up and possibly have some overall adhesion effect by having a clear layer of varnish overlaying the whole painting.

    I would not use the oiling out method that you mention because linseed oil will darken over time and for the same reason, I would not use an alkyd based medium. Alkyd mediums are non-yellowing in relation to linseed oil but they are intended to be used as an additive to paint rather than as a clear coating, which once again would be likely to darken slightly as it aged.

    I feel that the best thing to do is to apply one or two coats of Chroma Solvent Finishing Varnish in the satin version which will allow you to make a fairly substantial varnish layer without creating an unpleasant gloss.

    I can see that you would like a sealing coat so that a strippable varnish like the Chroma varnish could be removed at some later date. Because of the tendency to yellowing of linseed oil or an alkyd medium I think it would be wise to forgo that option and simply varnish the painting.

    Maybe you could consider do some retouching repairs before you varnish but I can't say definitely without seeing the image.


    I could use a traditional oil painting medium (no alkyd/acrylic resins) using the 'oiling out' method which in turn requires quite a lengthy amount of drying time prior any final varnishing. My question if this old traditional oiling out method would act as the best binder/sealer/stabliser choice against modern alkyd/acrylic (flexible) based medium glazes that are now available.

  2. comment_2_9951

    MetinYilmaz commented on April 7, 2012, at 12:40 am.

    Hi, how is the result when we use Archival mediums with other brands' oil paints (not mediums)?