Watermarks – 8 Causes

And how to put things right

Ever had this? So you’re tracing – tracing or strengthening: painting lines with a tracing brush – and your line itself looks good enough. But around the line you see a watermark: a halo, where water from your tracing paint seeps out. Ever had that?

Watermarks are bad for stained-glass painting

Then it dries of course: the watermark disappears. But next thing is, it often leaves a tidemark.

Now here’s the point: you mustn’t put up with watermarks – they’ll give you problems later on.

Big problems

For example:

  • When you shade by softening trace-lines (a technique you really need to master), your lines won’t soften evenly like they should.
  • Later on, these watermarks will also make it difficult to soften your highlights – the tidemark gets in the way.

And another thing: uncontrollable effects aren’t clever

Me, I don’t like effects I can’t control – effects I don’t intend to make.

Sure, serendipity is great: we can discover a whole load of things by chance.

And sure, if we never take a risk and sometimes fail, we’ll never learn.

But that’s not what I mean. What I mean is: when I’m painting for a client, I already know what I want.

And if something happens which I’m not in charge of – like watermarks / halos for example – actually I just don’t like it.

Watermarks are for banknotes

Watermarks are what you want to see on banknotes. And halos look great on angels.

But you don’t want them when you trace.

So what’s gone wrong to cause the watermarks?

One or several of these 8 points. Now I just want to write down everything I can think of so it’s all in one place.

#1: tracing paint too watery

Tracing paint too watery on your palette: this is when there just isn’t enough glass paint in your water to slow down its natural rate of flow.

The answer is, mix in more paint and darken up throughout. (Don’t go overboard: sometimes it just takes a small amount to put it right.)

Once your tracing paint is thicker, its water-content is far less prone to separate and seep.

Stained glass tracing: often, a thicker paint is helpful

I often work with quite a thick, dark mix like this

When I was learning, I often got this wrong; I always made my paint too wet. What I thought was, “It must be wet, else it won’t flow”.

I know better now: I’m confident enough to make my tracing paint far more viscous. Frankly, the last thing I want is tracing paint that flows “by itself”. Now my tracing paint just flows when and where I put it. The reason is: it isn’t watery, it’s viscous.

#2: badly mixed paint

Badly mixed paint on your palette: this is when your tracing paint is watery in parts, more viscous in others.

The darker, more viscous portion might well be excellent in itself, but the watery portion will push and flow too fast.

When you get both kinds on your brush, that’s a certain recipe for trouble.

The answer is, spend more time mixing with your knife or brush: make sure your tracing paint is the same viscosity throughout.

stained glass painting - grind the paint

Stop and grind or mix whenever you have to

#3: brush too wet

Brush too wet: so you often rinse your brush in water (which is good), but you neglect to flick off excess moisture (which is bad).

Now, no matter if your paint itself is perfect, you’ll still hit difficulties when you try to trace.

The problem is, the water in your brush won’t properly integrate with the tracing paint you want to work with: another cause of halos around your trace-lines.

The answer is: rinse then flick your brush before you load it. (Gently flicking doesn’t disturb the brush’s shape.) You want a damp brush (not a wet one).

#4: wrong brush

Wrong brush: too big, or wrong shape.

Could be you just need a finer brush, or a brush which holds less paint (Remember: the more paint it holds, the greater the downward pressure on the flow.)

#5: too much pressure

Good tracing:

  1. The right consistency of well-mixed paint,
  2. The right brush, and
  3. The right pressure for whatever consistency of paint and brush you have.

Yes, your paint and brush can be all in order, but if you push too hard, you’ll cause too much paint too flow.

So try a lighter touch. Try tracing with just the tip.

Stained glass painting: try tracing with just the tip of your brush

Try tracing with just the tip of your brush

With less pressure on the brush itself, you may also need to slow down in order that your paint has time to flow.

But actually, slow tracing is usually the best.

#6: undercoat not properly dry

A wet or damp undercoat can’t offer enough resistance to the water in your trace-lines.

stained glass painting: wet undercoat

You can see this undercoat is too wet to trace on

The answer is, make sure your undercoat is fully dry before you trace on it.

Maybe that’s obvious. But it brings us neatly to the the essential role of gum.

#7: not enough gum Arabic

This is so important. Whenever there’s not enough gum Arabic in your glass paint, two things happen (because gum Arabic is glue):

  1. Your undercoat can’t dry hard enough to resist the water in your tracing paint.
  2. Your tracing paint itself won’t bind together like you want it to.

So, when you add more gum, again, two things happen:

  1. When it’s dry, your undercoat will “set” more firmly than before, resisting seepage from your tracing paint.
  2. Your tracing paint itself (because it has more glue in it) will be less prone to separate. The gum in your paint helps hold your paint together while you paint with it.

I especially love this 7th point: some artists try to drive a wedge between art and science. But – no surprises here – their raw materials just continue to obey the natural laws of chemistry and physics.

Want more tips like this?

These are really valuable points. If you haven’t got our e-book, you’ll find lots more techniques right here.

#8: our outlook

This last thing I want to say is different from the other 7.

It concerns our outlook.

For example: me, I make all kinds of compromises when it comes to sorting out priorities with other people.

But I have learned never put up with anything that stops me achieving my best with anything I choose to do.

So if something’s not working as it should, I nearly always stop and put it right.

This comes from the days when I played the violin. (Back then I thought that’s what I’d do in life.) If my violin was out of tune, I’d always stop and tune it.

If you’d be listening to me, you’d have known my judgement was correct.

But I reckon you’d be surprised how many players think they’ll put it right just by carrying on

So now with glass painting, I don’t let anything block my path.

  • If my brush is old, I throw it out.
  • If my paint is drying, I stop and mix it.

In general: if something’s not working as it should, I’ll always stop and fix it. Doesn’t matter this takes me hours: this extra knowledge is valuable to me.

Stained glass tracing

If it’s not happening like this, I stop and put things right

That’s how I’ve learned to be.

Sure, people call me hard-nosed. But the way I see it, far too many artists don’t put up a proper fight when things aren’t going right. They just accept things. They seem to me to assume that’s just the way things must be:

Oh dear, water-marks – never mind: must just carry on and finish my tracing …”

But I reckon that’s not the right approach. It’s not the right approach at all.

I’m an absolutist here. Plus, I’m methodical.

When you combine the two, and you’ll soon be writing to me with all the great discoveries you yourself have made.

Lots more techniques and tips right here.

That’s all for today: if you enjoyed this post or found it useful, please share a link. Thank you!

9 thoughts on “Watermarks – 8 Causes

  1. Hello Stephen,

    On the same note, I recently did a painting with oil. After firing, it looked rather gritty. I expected it to be nice and even. Too much oil? Firing temp. too low? Or all of the above? (The glass was baroque type glass.) I’d appreciate your comments. Thanks!


    • Can you e-mail me a photo? Not yet having seen it, my instinct is to say: contamination e.g. in the brush or paint or medium. But maybe the photo will suggest something else. Anyway, David or I will certainly write something about contamination: it’s important to avoid (even if this isn’t what accounts for your gritty firing) and we haven’t dealt with it before.

  2. Thank you for all of this advice, Stephen, especially so when you two are overwhelmingly busy with your own projects.

    Regarding the amount of gum Arabic: is there a preferred ratio of gum to pigment You’ve probably mentioned this before, but my memory isn’t as viscous as it used to be … (That was intended as sort of a joke … which is pretty bad when I have to clarify!)

    Warmest Regards to yourself and David,

    • Hello John,

      If we make a brand-new lump of paint, we’ll start with around 3 well-heaped tablespoons of pigment and 1 teaspoon of gum Arabic (all bound together with as little water as necessary). This ratio suits most painting that we do. But … sometimes more gum is useful.

      All the best,

  3. Hello Stephen,

    I went through this problem as well. (Like you say, these watermarks will clear all the undercoat when you soften the highlights.)

    But I realised that my problem was in the gum Arabic quantity, as you also said. In the beginning it was a little bit difficult for me to determine the exact quantity. You must test your paint on the light box until you realise that your paint doesn’t leave watermarks.

    I think it depends a little on personal attention to detail. Now I haven’t had that kind of problem.

    But you must mix your paint. The constant mixture on the palette, it is crucial to be able to work without unpleasant surprises.

    It’s always pleasant to receive your posts.

    Have a good week!

    • Hello Fábio,

      You make a wonderful and useful point: it is actually one of the tests you should do with a freshly-made lump of glass paint – namely: make sure you can easily trace with it without leaving watermarks.

      You also mention personal sensitivity and constant mixing on the palette: for me, and I know from our conversations it is also the same for you, it is one of the joys of glass painting that our medium – this paint – demands our constant supervision and adjustment. Tiny changes, constantly.


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