The best advice is to leave the white of the watercolour paper for your highlights and white areas but sometimes this isn’t possible and sometimes you just forget, so it’s useful to have the option to add white over your paint at the end.

I’ve tried a few whites over the years with varying degrees of opacity, so I decided to do this comparison of those that I still have. 

Each has its pros & cons, some are more opaque, some better for highlights, others better when a larger area of white is required, some are simply more convenient or less expensive.

The whites I used in the test are: Acrylic (I don’t normally use acrylic on watercolour but happened to have some on hand), Gouache, Uni-Ball Ballpoint, Uni-Ball Posca, Kuretake Ink and Dr Martin’s Ink.

I did the test on Bockingford 535g ‘Not’ watercolour paper using a selection of watercolours from the Winsor and Newton Cotman range to see how the various whites performed on different colours. I used a ruler to get straight lines from the white pens and masking tape for the acrylic, gouache and inks.

The attached photo shows the results.

The acrylic was disappointing, I had to lay it on thick to get the desired opacity, normal application resulted in the underlying colour showing through. £6.95 for a 150ml tube on Amazon.

The Gouache was OK but appeared to be less opaque on the grey & black than on the colours. £6.36 for a 14ml tube on Amazon.

The Signo pen with the broader nib worked better than the finer one as regards opacity, but the line tended to be uneven for both. However, these pens are convenient to use and inexpensive and can be useful for small highlights. Broad nib £4.19/pen, Fine nib £6.26/pack of 3 on Amazon.

The Posca pen gave a thicker line than the Signo but was less opaque. In my opinion not the best for highlights or larger areas. £4.89 on Amazon

Both the two inks gave a reasonably opaque finish. Dr Martin’s flowed better than Kuretake but neither worked with a dip pen unless they were thinned so much that they lost their opacity, so I applied them with a brush. There’s not much to choose between them and I think that both could be used with a fine brush for highlights or a larger brush for greater coverage. Overall these two worked better than the other options but are the most expensive at £13.94 for a 30ml jar of Dr Martins and £11.98 for a 30ml jar of Kuretake on Amazon. However, I’d expect them to last for years if they’re only being used to add small areas of white to a watercolour painting.

In conclusion, I think I’ll continue to use my Signo pens for small highlights because of their convenience but will probably make more use of both white inks for their greater opacity. I’m not suggesting that these are the best available out there, but they are the best of what I currently have.

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