Glazing Medium vs Flow-Aid vs Thinner for brush-work
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Thread: Glazing Medium vs Flow-Aid vs Thinner for brush-work

  1. #1

    Default Glazing Medium vs Flow-Aid vs Thinner for brush-work

    I am getting back into painting minis for the first time since I was a teenager and trying to do some research in advance so I don't make all the same mistakes I used to. I have some old citadel paints which I have supplemented with Vallejo.

    One of the major things I see from the forums is that I should thin my paint as a matter of course (not just for washes), and often use multiple thin layers of paint in preference to a single thick layer. I see that people mention a variety of additives including thinner, medium (matt/gloss for different finish), glaze medium for transparency, flow-aid, and retarder, as well as plain water of course.

    I understand that the mediums are pigmentless-paint designed to dilute colour but not consistency, so I picked up some Vallejo glaze medium (I didn't want to alter the finish too much with matt/gloss). However, I am not sure how this compares to thinner - they both sound like they thin down paint and make it more transparent. What is the difference please? If thinner thins down the consistency as well, how is that different to using water?

    Plenty of people recommend flow-aid and retarder, but apparently Vallejo glaze medium has some of the qualities of these, so I am wondering if I should invest in these extra materials, or is Vallejo glaze medium a 'fix-all' additive which some people suggest? Of course, I may end up having to buy lots of glaze medium if I use it all the time for all purposes so it may be best to use different products for different scenarios if it's more economical.

    A few other questions
    1) Do people usually mix BOTH water and glaze medium, or just one or the other?
    2) Some of my old citadel paints are dried and need some work adding liquid (quite a lot in some cases) - should I use water or glaze medium or something else to attempt to bring them back to normal condition? Some people recommend citadel Lahmian medium but I understand this is similar to Vallejo glaze medium.
    3) I know everyone is hesitant to give firm advice on to what extent paint should be thinned down, but I would be grateful for a general pointer for normal application of the first colour on top of the primer (not glazing/tinting/washing) i.e. how do I know if the paint I am using is too thick?

    Thanks so much all - really grateful for any tips!

    P.S. I also created a wet palette using tupperware, kitchen towel and baking-paper - I haven't yet used this but I mention it in case it makes a difference to what other additives to use. I understand this will automatically cause water to be sucked up into the paint so other products perhaps less necessary?

  2. #2


    you don't really need any of these additives. For acrylics water is enough after you learned to use it correctly (thinning, brush control).
    That said they can help do things faster or can be useful if you don't have the experience yet.
    Think of using them to be similar to training wheels for bikes (unless they are used for some specific purpose, like Flow-aid+Airbrush, or gloss medium to simulate materials)

    Thinner: it's basically the same binding agent that's in the paint, so using this to dilute the paint helps by having the same consistency. Also helps avoid some of the difficulties of water, like drying in rings (can be avoided by not letting the paint pool). One 'fun' thing is that with airbrushes it makes the paint dry faster, so more cleaning of the needle is needed.
    Flow-Aid: help lower the surface tension, so paint flows better. On the surface it leads to a more even coat. Best use of it is in Airbrushes, where it helps paint atomize in a more uniform way
    Retarder: slows drying time.
    Glaze medium: in theory it helps dilute pigments, so the paint becomes more transparent, but the vallejo glaze medium is more like a mix of thinner+retarder+bit of a satin medium.

    1. when I use (rarely) glaze medium, I always mix it with water
    2. you could try thinner / matt medium (same as lahmian from GW, but better priced) but at the end you may have to invest in new paints.
    3. with vallejo paints I use there as a general rule:
    - basecoat: undiluted (Vallejo Air Color and/or fast TTQ work) to about 1:1 mix (VMC colors mostly)
    - layer: about 1:2 (paint: water) mix
    - glaze: about 1:5-1:8 mix
    As a general rule for what you asked: drag your brush through the paint, if it flows back again and no brushmark can be seen, it's ok.
    For layers a good trick: have a piece of newspaper, if the paint covers relative well while you can still read the text (but now with a background color that's the paint you used) it's about ok.
    Same for glazes: you should be able to read the text, while it has a hint of the color you used as a background color

    wet-palette: your choice. As I started: you don't really need any of the additives.
    Forgot, that it works again.

  3. #3
    Senior Member Ghool's Avatar
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    Calgary, AB. Canada, eh.
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    If you're just getting back into it, all you need is paint and water.
    As you get more comfortable again, then consider getting a few additives.
    Don't think because so many people use additives that they are needed at all.

    30 years after the fact, and I still only use paint and water for about 90% of applications.

    MAXXxxx has pretty much covered it all, so there's not much to add.
    But I'll link a couple things I did while ago that might help.

    You can watch my videos on YouTube -
    And you can also support me on Patreon -

  4. #4


    I'm not going to rehash the technical side of things.....this is just my ten cents worth. I too mostly use water to thin my paints because I paint by layering with dilute paint for my colour transitions. Most of the time it's ok as I keep my brush just wet and don't want to sit there for ages between layers if I was to use a retarder. Using just water I can have successive layers dry quickly. The only time I ever use a drying retarder is if the weather warms up and I need it to stop paint drying in the brush. The wet pallet also helps keep paints cold and therefore useable for much longer requiring minimal retarder being used. In warmer weather misting the paints on my wet pallet with water also helps.

  5. #5


    Thanks this has been really helpful. I had good results restoring old citadel paints with hot water and a bit of thinner (except an old burnished gold metallic which now seems to be very grainy and textured and is probably now useless - I understand metallics are known to be more difficult to restore). I’ve bought a whole load of Vallejo paints to supplement them but it just seemed a shame to bin so many old paints, many of which were over half full.

    Tip for painting on the newspaper to judge thinness is great - I’ve started using this. I will hold off on other additives for now.

    I am enjoying how much longer paint stays usable in the wet palette (especial since I am often called away from painting by family) but I think I may have over-wet it as it seems to be thinning my paints a lot. When I touch the brush to the model a whole lot of watery paint immediately runs off and acts like a wash running to the recesses. I hope reducing the water in the palette will fix this.

    My next task is seeing which of my old brushes are still usable. Some look good but many have dried paint from years ago. I’ve left them soaking in Brush Cleaner from the local art store and hoping this may get the old paint out of the brushes (although no results after he first few hours of soaking). I’ve also ordered some Mastersons Brush Soap. Is it possible to restore an old brush which hasn’t been cared for properly and is now stiff and lost its point?

    Speaking of brush care, I’ve been using a two-pot rinse - one for the first really dirty rinse and the second with cleaner water (changing water after using a metallic paint). I plan to do a proper clean with Brush Cleaner and Mastersons every couple of weeks or maybe month. Just wondering, Do people add anything to the rinse water to help it rinse paint off? (Like dish soap perhaps?)

  6. #6


    As much as it hurts it's often best to ditch the paints that have required extensive work to bring them back. They may look good in the pot but really interfere with getting a top finish.
    I don't understand how water is getting into your paints unless you have added excess water to your sponge or kitchen towelette paper layer that is then flooding onto your baking paper layer the paints are sitting on. Add water to the paper towel layer until it JUST starts to drip. Then apply baking paper on top. That will ensure its wet enough to keep your paints fluid. If I need to use additional measures to keep the fluidity of the paint that's when I lightly mist the paints with water.
    As for cleaning brushes I will leave them suspended in a pot of Vallejo brush cleaner. Sometimes for a few days. They then get a wash under the tap after I have massaged the brush soap you have bought into them. Like paints old brushes are beyond help sometimes. If they don't respond to a deep soak and clean they are sadly knackered. Use it as a great time to invest in a new brush. I only deep soak the brushes when they need it and that depends on usage. I use the Mastersons soap at the end of each paint session as they need to be looked after to prevent advanced issues.
    Last edited by bullfrog; 08-13-2018 at 10:55 AM.

  7. #7


    I’m just watching the videos posted above. What is the difference between Thinner and Matt Medium? People seem to suggest them for roughly the same purpose I.e diluting colour without diluting consistency. Are they both useful for making washes and generally thinning?

  8. #8


    basically matt medium also has a matting agent in it. Can kill metallics (makes it look simple grey) or other effects (like the satin look of leather).
    Thinner dilutes like the matt medium, but doesn't change the finish.

    Of course if you matt varnish (+add gloss where it's needed) the figure at the end, than it's not an issue.
    Forgot, that it works again.

  9. #9


    Thanks - I’ve already got some Vallejo thinner and Matt varnish so I won’t bother investing in Matt medium as well for the time being.

    When rinsing your brush during a session, do you add anything to the rinse water to help remove paint? There always seems to be quite a lot of paint left on the brush even after extended shaking in the rinse water (and paper towelling).

  10. #10


    not me. I use the brush soap for maintenance every few months, but other than that I use just plain water. During session and after session too.
    If you have quite a lot of paint after rinsing there could be 2 causes:
    - paint is too thick / partly dried on the bristles
    - you dip it too much into the paint. The paint should be only on the tip + up to about half of the bristles. If it's up to the ferrule (harder to get rid of paint from here), than it's definately too much.

    edit: I'm pretty sure ghool has videos on brush care/use too.
    Last edited by MAXXxxx; 08-14-2018 at 06:39 AM.
    Forgot, that it works again.

  11. #11


    Thanks - I am still getting used to thinning so probably you are right that my paint is too thick.

    When cleaning brushes, I see some people recommend Isopropyl alcohol. Is this doing a similar thing to standard brush cleaner fluid or is it worth owning both? I’ve had brushes soaking in brush cleaner for about 36 hours now with good (but not total) success in removing old paint.

  12. #12


    Isopropyl alcohol is okay to use with synthetic brushes, but not with natural hair brushes (or at least not recommended). I could be wrong about that though but I have heard it bandied about before.

    I do soak my synthetic brushes in Isopropyl alcohol and it will remove the acrylic and primer paint from them. On the same turn, if you are using synthetic brushes I don't believe that the Masters brush soap works on synth brushes as well as natural hair.
    Last edited by ekipage; 08-14-2018 at 08:18 PM.

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