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Old 03-13-2018, 12:03 PM
grisbear grisbear is offline
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Noob: What is a solvent and what is a medium?

Hi! If there's a listing of "noob questions" I'd surely love to read through it, but I couldn't find one.

I come from watercolor and I think this has left me very confused. I feel like people are often comparing oil painting solvents and mediums to the water in watercolor -- "You know how you get more water in the paint to thin it out? It's like that! You know how you use water to clean the brushes? It's like that!"

In watching tutorials and things, I feel like maybe this might have been an oversimplification that's leading to confusion in me.

So -- what is a solvent anyway? What is a medium anyway? How are the different? When do I use solvents versus when do I use mediums?

Basically, I know I need to mix *something* in with this paint because it's very thick and impasto and that's not the look I'm going for -- I turned to oil due to its blend-ability, slow drying times, and opaque layering. I have OMS, linseed oil, and liquin and I haven't a clue when to use which.

Also somewhat related -- in watercolor, the biggest thing people say all the time is to "just try it out on some scratch paper!" since watercolor is, comparatively, pretty cheap to use. Is this something oil painters do? What is your "scrap" paper? Both the canvas and panels I've used seem a bit expensive to just try things out on.
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Old 03-13-2018, 01:44 PM
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Gigalot Gigalot is offline
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Re: Noob: What is a solvent and what is a medium?

White Spirit is a solvent and it can evaporate without having residue. Linseed oil is drying oil, it can't evaporate, but can polymerize and form film. If you take 50% Linseed oil and mix it with 50% White Spirit, you will prepare "medium".
Medium is a mixture of solvent and oil. Using medium, you can make oil paint less viscous without adding too much oil into it. But if you go baldheaded at paintings, then you are working "solvent-free"!

Last edited by Gigalot : 03-13-2018 at 01:54 PM.
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Old 03-13-2018, 02:07 PM
JCannon JCannon is offline
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Re: Noob: What is a solvent and what is a medium?

Actually, these terms are more difficult to define than many here might think. In oil painting, we take our definitions from tradition, not from the dictionary.

A dictionary will define "solvent" as any liquid in which a solute can be dissolved. A "solute" can be a solid or another liquid, usually a thicker liquid. Thus, water can be considered a solvent in watercolor painting. In oil painting, both oils and turps can (by this definition) perform the solvent role.

But that dictionary definition is not the definition usually used by artists.

In oil painting, "solvent" usually refers to turpentine or odorless mineral spirits (OMS). Those are the big two, although some artists use more exotic concoctions, such as a product called Neutral Thin (which I use.)

Turpentine (informally called "turps") is considered the most aggressive solvent in terms of dissolving power. That is to say: If you want to dissolve a resin such a gum elemi, you need let it sit for a while in a jar of turpentine. OMS won't work -- at least, not as well.

Turpentine differs in quality. The stuff you get at hardware stores often smells awful; the good stuff smells like Christmas trees.

Turpentine and OMS can be used to thin oil paints during application. They are also used to clean brushes.

The important thing to keep in mind about turps and OMS is that these liquids evaporate. Usually pretty rapidly.

Artists do NOT consider oils and resins to be solvents, although (as noted above), the folks who compile dictionaries might not agree with that opinion. Oils and resins do not evaporate: They harden. That is the main difference between an oil and a solvent.

Like solvents, oils are used to thin paint to make it easier to apply. Some people even use oil for the purpose of brush cleaning.

The oils used in painting are called "drying oils" because, well, over time, they dry. They get hard. Some oils (such as the vegetable oil you probably use in cooking) never dry and thus must never be used in painting.

The two most popular drying oils used in painting are linseed oil (a.k.a. flax seed oil, the same stuff sold in health food stores) and walnut oil (which is also sometimes used in cooking, even though it's a drying oil).

Less common drying oils are poppy, safflower and sunflower. These latter oils come in both drying and non-drying varieties, so you probably shouldn't paint with the stuff you buy in grocery stores.

Linseed is the most popular oil in oil painting because it dries the most rapidly and because the film is very stable. However, it yellows. Paintmakers often use walnut, safflower or poppy to make light-colored paints, because those oils do not yellow so badly. The trade-off, of course is the drying time, which can be infuriatingly slow.

There are various methods for "cleaning" linseed oil which supposedly renders it less likely to yellow. That's a huge topic of discussion in its own right.

Now we come to your ultimate question: What is a "medium"? Within oil painting, a medium is any liquid you use to thin your paints, or to modify the paint in some other way.

There are artists who want to extend the paint so that a little goes a long ways. Some artists want the brush strokes to be emphasized, while others want the paint to level out. Artists who like to glaze want a medium that allows them to spread a tiny amount of pigment in a thin, subtle fashion. Some artists like a medium that makes paint glossy; some prefer a matte finish.

Different artists use different mediums to achieve these effects. Every artist settles on his or her own medium, after a period of experimentation.

Most mediums mix a solvent and an oil. A simple 3:1 ratio of turpentine to linseed oil is very common.

It's also pretty common for artists to include a little bit of resin into the mix -- copal and damar used to be frequently seen in artists' studios, although not so much these days. There are also more exotic additives, such as gum elemi and canada balsam.

When I ran across an old book that described a medium incorporating frankincense, I just had to whip up a batch. Works well, and smells right purty!

By this point, you are probably thinking: Is it possible to have a medium that is just solvent? Yes. I've painted large patches using nothing but Neutral Thin as my medium. Many here will say that you must never use pure solvent as your medium, because the paint film won't be strong enough. I'm not so sure about that claim. Remember, the paint already has a lot of oil in it -- besides, the final work will receive a coat of protective varnish.

It is also possible to use nothing but oil as your medium. Some artists are strong advocates of "solvent free" painting. Health-wise, some people are very sensitive to solvents.

If you want a layer to dry fast, use a solvent-heavy medium. The oilier the medium, the slower it dries. The principle of "fat over lean" usually requires the artist to use a lot of solvent in the lower layers and an oil-heavy medium in the upper layers.

I have not even mentioned mediums incorporating alkyds, a relatively new factor. The main advantage of putting an alkyd in the medium is rapid drying. Some artists hate alkyds; some love them.

Apologies if this response was overly long...

Last edited by JCannon : 03-13-2018 at 02:11 PM.
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Old 03-13-2018, 02:24 PM
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Re: Noob: What is a solvent and what is a medium?

JCannon's answer is very good overall, especially concerning the definition of solvents.

I do believe many would say a "medium" is anything that modifies the handling or properties of your paint though, as there are several "solid", or semi-solid mediums on the market (gels, wax, or even powders). It is not restricted to being just a liquid that modifies your paint properties. The purpose being to make your paint handle, dry, or look the way you desire.

Edit: As to your question of what to use for a test surface, there are any number of surfaces you could use. Mostly I use cardboard, paper, or hardboard panels bought from the hardware store, prepared with a size or other dilute glue (sometimes I will texture the surface with a chalk or gypsum gesso). This is similar enough to the surfaces I generally paint on to get a feel for how something will react on a final surface. For paint saving I will sometimes scrape all the left over paint into a little tiny foil square and fold it up to use these color "packs" for later as a neutral to reduce the intensity of pure tube paint.
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Old 03-13-2018, 03:31 PM
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Re: Noob: What is a solvent and what is a medium?

I'll try to answer your question as directly as I possibly can.

A "medium" is any form of liquid material that can cause your paint to handle precisely the way you want it to handle for the specific effect you are attempting to create with oil paint.

That being said, some "mediums" are more appropriate to use than others, and for many different reasons.

Using a solvent alone, by itself, as a painting "medium" is not very appropriate, because a solvent can wash the binding oil off of each particle of pigment, causing the paint to become underbound--a condition in which the paint will chalk off in a powdery form, even after it has dried. This is considered a very weak paint film. While the solvent may cause your paint to handle wonderfully, it is not an appropriate item to use by itself at a "medium", for the reason I have mentioned.

Using a drying oil alone as a painting "medium" is usually not very appropriate because it can create very long drying times, and often impart a very glossy, sticky appearance to the surface of the painting, even after it has dried.

The best advice I could offer would be to use a combination of the two--a drying oil, such as Linseed Oil, or Walnut Oil, AND a solvent, such as Turpentine, Odorless Mineral Spirits, or Oil of Spike Lavender, mixed together.

Usually, just one, or perhaps two drying oils mixed with one solvent creates a very usable, and sound medium that will cause your paint to handle wonderfully, as well as create a sound, durable paint film, when mixed with your paint.

Although it is not carved in stone, it is a sound practice to limit your use of a painting medium to no more than approximately 20% to that of the paint with which you are mixing it, by volume. Of course, for special effects such as painting hair, or long grasses, or telephone lines, you may need to use a bit more medium to achieve such effects, and to make the paint flow, and believe me when I add that your painting will not suffer any substantial ill effects by doing so.

I use a specific painting medium that I invented for my glazing, and layering process, and I mix it myself from a couple of drying oils, a resin, and a solvent. It has worked well for me for many years, now, and because I engineered the recipe to perform exactly as I want it to, it performs precisely as I want it to.

Many alkyd mediums (such as Liquin, and Galkyd) tack up much too fast for my use, and cause my palette to become prematurely sticky, tacky, and "draggy", while I'm working with it. It is for this reason, primarily, that I avoid using alkyd materials as mediums with my traditional oil paints.

Long story, short: A solvent is a solvent, a drying oil is a drying oil, and I don't consider either of them to be a "medium" when used by itself. But, when mixed together in an appropriate ratio, they can be made into a very workable, durable painting medium.
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Old 03-13-2018, 03:43 PM
grisbear grisbear is offline
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Re: Noob: What is a solvent and what is a medium?

Wow all of these replies have been so helpful! I see exactly what I am doing now and exactly why I'm getting the yucky results I have been -- I've been using OMS on its own to "thin" down the paint just as one would use water in watercolor -- to dilute the color. It's made a streaky weird mess. I've also used liquin on its own, but it took a hellofalot of liquin to get the paint to stop being toothpaste and start moving easier. And I used linseed oil on its own which felt great but is totally why half (only half, the other half I used OMS on its own) of the painting is still currently drying.

You all are AMAZING! Thank you times a million! I'll grab one of those 25cent glass containers at the hobby/art store and start mixing the OMS + Oil together in differing amounts and practice it out on some wood from the home depot.
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Old 03-13-2018, 04:00 PM
p_nathan p_nathan is offline
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Re: Noob: What is a solvent and what is a medium?

definitions:

solvents dissolve the bonds in oil. too much solvent reduces the paint to dry pigment & bits of what used to be oil that can be brushed away.

mediums are any additive, including typical oil solvents.

oil painters often have a side hobby of playing with mediums: things like waxes, distilled tree resins, heated oils, different dusts (silica, chalk, etc), unusual plant oils, etc all have been used for different purposes.

liquin is a fast-dry alkyd, which is an additive that can be roughly used like "oil".

Mediums are generally used for specific effects - visual, handling, etc. Different strokes & styles for different folks. The only limitation here is, in practice, the technical soundness of the paint (i.e., will it crack, melt, turn into dust etc). Your additives are, btw, fine, with the only risk being adding too much solvent.

you can buy canvas paper, which is a cheap way to "Scribble".

best of luck.
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Old 03-13-2018, 05:18 PM
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Re: Noob: What is a solvent and what is a medium?

Quote:
Originally Posted by grisbear
Wow all of these replies have been so helpful! I see exactly what I am doing now and exactly why I'm getting the yucky results I have been -- I've been using OMS on its own to "thin" down the paint just as one would use water in watercolor -- to dilute the color. It's made a streaky weird mess. I've also used liquin on its own, but it took a hellofalot of liquin to get the paint to stop being toothpaste and start moving easier. And I used linseed oil on its own which felt great but is totally why half (only half, the other half I used OMS on its own) of the painting is still currently drying.

You all are AMAZING! Thank you times a million! I'll grab one of those 25cent glass containers at the hobby/art store and start mixing the OMS + Oil together in differing amounts and practice it out on some wood from the home depot.

A very good beginning painting medium is a mixture of equal portions of Linseed Oil, and Odorless Mineral Spirits.

When I mix my ingredients for my painting medium, I use one of those small, plastic measuring cups that I buy at the pharmacy by the dozen, or so. They have units such as Tsp., ml, oz., and drams indicated on the side of the cup. I usually use "drams" just because that is a convenient measuring amount.

I usually mix the two ingredients together in the measuring cup, and then I pour the mixture into a discarded, glass, or plastic bottle, such as a used Linseed Oil container that has a cap, which I use as a "reservoir" for my mixed medium. It will keep for months in a closed container such as that. After pouring my mixture into the bottle, I shake it for awhile, long enough to eliminate the visual striations that form, indicating that the ingredients are not quite mixed thoroughly. Once it appears clear of those striations, it is mixed, and ready to use. I keep it capped, when not in use.
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Last edited by WFMartin : 03-13-2018 at 05:20 PM.
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Old 03-13-2018, 06:09 PM
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Lazarus E Lazarus E is offline
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Re: Noob: What is a solvent and what is a medium?

my advice.
dont buy any pre-medium or gel. make it by yourself.
linseed oil turps and damar varnish. work well and the same as all mediums. or even better.
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Old 03-14-2018, 02:47 AM
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Re: Noob: What is a solvent and what is a medium?

Quote:
Originally Posted by grisbear
I've been using OMS on its own to "thin" down the paint just as one would use water in watercolor -- to dilute the color. It's made a streaky weird mess.
Just study wet-in-wet oil painting technique and you will get the advantage of oil over other mediums. But if you really need to have extremely fast drying underlayer, then do it with acrylic paint. Oil paint needs time to work.
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Old 03-14-2018, 09:48 AM
TomMather TomMather is offline
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Re: Noob: What is a solvent and what is a medium?

Some good information here from knowledgeable painters. Iíll add a few things based on materials that I use. First, I paint relatively fast, usually on smaller canvases, so I prefer faster drying times between layers.

I use odorless mineral spirits, specifically Gamsol, to thin my first layer of paint - usually a single color (such as ultramarine blue) to block in the composition and darker values. This dries quickly so I can start the second layer right away or whenever Iím ready to work again. I also use OMS to clean my brushes. I keep the OMS in a covered jar to limit the fumes.

I use an alkyd medium, Galkyd Light, as my preferred medium. I like the way it makes paint flow and it dries quickly enough that I can apply another layer of paint in 1-3 days, depending on the colors. Some colors, such as titanium white and alizarin crimson, dry very slowly, even with an alkyd medium. Other colors, such as burnt umber and ultramarine blue, dry much quicker. I also use Galkyd in final layers, but usually less. Itís important to clean brushes soon if you use an alkyd medium so it doesnít start drying on them.

One question that I have for those more knowledgeable, is it OK to use an oil- based medium (eg, linseed or walnut) for final layers in a painting that you started using an alkyd medium? I donít mind using a slower drying medium in my final layer because Iím done working on it by then. I used to use linseed oil as my primary medium but got frustrated by the slow drying times, and I messed up some paintings by working on them too quickly before layers had adequately dried.

Last edited by TomMather : 03-14-2018 at 09:50 AM.
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Old 03-14-2018, 11:21 AM
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Re: Noob: What is a solvent and what is a medium?

Quote:
One question that I have for those more knowledgeable, is it OK to use an oil- based medium (eg, linseed or walnut) for final layers in a painting that you started using an alkyd medium? I donít mind using a slower drying medium in my final layer because Iím done working on it by then. I used to use linseed oil as my primary medium but got frustrated by the slow drying times, and I messed up some paintings by working on them too quickly before layers had adequately dried.

I know that others will disagree with me on this answer, but I believe it is best to stay with an alkyd medium for the entire painting, especially one that you have built in layers.

The reason is that alkyd mediums seem to have a characteristic all their own, in terms of drying. They dry fast, like a lean medium, but yet they remain flexible while drying, like a fat medium. To me, this makes it nearly impossible to determine just where it is the most appropriate to apply an alkyd-laden layer of paint within the layers of more traditional paint, while yet observing the fat-over-lean principle.

To avoid such occurrences as cracking, or delaminating, I believe I would stick with the alkyd throughout the layers of the painting. Just my thoughts.
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Old 03-14-2018, 01:23 PM
grisbear grisbear is offline
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Re: Noob: What is a solvent and what is a medium?

What's an alkyd medium? Is it a pre-mixed thing? Or do I need to mix it with OMS to make it a real medium? And is liquin an alkyd medium?

I'm all for just sticking to linseed oil + OMS, just wanting to learn.
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Old 03-14-2018, 01:30 PM
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Re: Noob: What is a solvent and what is a medium?

Liquin is Alkyd medium. You can add 10% of it into 1:1 Linseed oil/OMS medium to increase drying and durability and improve sheen of paint layer. Working just fine.
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Old 03-14-2018, 04:51 PM
p_nathan p_nathan is offline
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Re: Noob: What is a solvent and what is a medium?

Typically alkyd mediums are premixed. The ones commonly talked about here are Galkyd and Liquin - each of those comes in a variety of styles - impasto, fine, normal, gel. M. Graham makes a walnut alkyd.

Many, many people love Liquin. Comes down to style, personal taste, and ability to withstand its smell - I think it smells like a petrol pump!
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