Paint Technical

Jul 10th, 2010 | | Paint Technical | 5 Comments

The World of Mythical Colour

Blue Green Gate

“A short time ago the artistic world discovered that on garden gates, farm fences, etc., there was a most lovely blue-green colour to be seen sometimes. This was Brunswick green in a state of dilapidation, and was showing that it needed re-painting. However, the colour was so lovely that many attempts were made to copy it in new paint. They all failed hopelessly. One cannot with paint fake the work of time”.

Brunswick Greens

These words of Basil Ionides, written in the 1930s, came to mind when I was talking to the owner of a large country house in Norfolk. Papers and Paints had been requested to devise a good blue colour such as (we were told) “had always been used on the gates and doors around the estate”.

Penrice Estate Doors

It doesn’t really matter, of course, that the blue that our client had in mind had almost certainly been a dark green when originally applied, for age had changed both the colour and the finish to produce a very pleasing result. A few years earlier, Basil Ionides had been more specific:

“Brunswick green outside is delightful after about three years, when it begins to become a lovely verdigris colour, but one has to suffer a dull colour till then, and this change really means that the old paint is perishing and new is needed.”

Several years ago I was commissioned to investigate the exterior paint colour in the National Trust’s famous Hidcote Manor Garden. For the last forty years the well-known bluish green has been used, however analysis has shown how this was a misinterpretation of the earlier Brunswick green. Perhaps surprisingly the original colour appears to have been brown.

Although modern paint no longer ‘chalks’ as an old lead paint does when it ages the colour still wanders. This can be seen on these stable doors after a few years exposure to the elements.

Stable Doors

Brunswick green ‘on the turn’ – the colour becoming noticeably bluer and paler.
NB also the flaking that is characteristic of an aged modern paint

In recent years blue seems to have become a popular colour for such surfaces even though it was seldom used on external woodwork in the past. Another colour with which it is confused is the one frequently referred to as the generic “French Château Shutter Blue” (could it be that there is more than one?) by several customers who have heard of our range of paint colours based on some of those seen across the various regions of France.

Blue Door and Shutters in the Languedoc

Even when aware of this phenomenon one often needs convincing. Whilst carrying out the analysis of the paint on the estate buildings at Culzean Castle, in Ayrshire, a red-brown door to the Kitchen Garden was seen to display an earlier scheme of greenish-blue.

Culzean Gardener's Cottage
Culzean Gardener’s Cottage

However, when the paint layers were examined under the microscope it became quite clear that the ‘blue’ was a result of the curious effect of ‘flooding’. This is when one of the pigments in the paint migrates to the surface – in the case of Brunswick green (composed of Prussian blue and chrome yellow) it is invariably the blue that rises as can be seen here:

Culzean Cross Section
A thin blue crust can be seen where the overlying red-brown has already flaked off. However where the red-brown is scraped off the underlying paint shows green.

Sulby Park: Green - Blue
Sulby Park Door

Here is another example recently encountered on a set of Soane-designed outbuildings in Northamptonshire. A slideshow of these buildings can be seen here.

Upper Face turned Blue
A cross section taken from the door above (note how the upper face is bluer than the rest of the layer)

This door on an Oxfordshire estate is just crying out for analysis. I’m sure that it was green

I have termed this phenomenon the “Penrice Effect” after the house where I first encountered it.

Cabmen's Shelter
Cabmen’s Shelter, Kensington
Notice how one side has been affected by the sun

There are many myths that have arisen in the world of paint and colour. A number of these will be addressed in subsequent blog posts.

Papers and Paints can be found here:

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Comments (5)

Xu EnNo Gravatar » 29. Jun, 2013

A fascinating article – but I think to describe the effect as ‘flooding’ is wrong – flooding is a specific term to describe what happens to the paint as it is painted and dries. A pedant could refer to the definition contained in ISO 4618-2:1999

I suspect this is a light (probably strong uv) effect – on one of your pictures (‘Sulby Park Door’) it appears that the part of the paintwork covered by the door when closed still appears green.

The easy test of this theory is by information you have access to – do the indoor parts of doors with paint remain green? or have they been affected in the same way too?

PatrickNo Gravatar » 29. Jun, 2013

Thank you. ‘Flooding’ was a word that I had read (possibly in Hess) to describe this action. Yes, of course UV has a major part to play and it doesn’t happen where the green is hidden from the light. You can see in the cross section how the Prussian blue rises to the surface.

Xu EnNo Gravatar » 30. Jun, 2013

Yes. I hadn’t paid so much attention to the cross sections but it’s clear from them that there is concentration of pigment at the surface. Excluding preferential wash out of yellow (which the surface concentration of Prussian blue tends to preclude) the idea of a flooding effect over a long period of time seems like a fair explantation – it well known that paints remain far from fixed solids even years after the can be considered dried.

I did initially wonder if your Brunswick Greens were very old and had a Copper Oxychloride based green which has an obvious route to copper carbonate (via atmospheric CO2 and water) / copper fatty acid salt (from reaction with the paints emusifiers) -these are green blue to deep blue depending on conditions of formation – mostly pH – generally very similar in hue to copper patina. The idea is attractive in its simplicity but I don’t think it is correct in this case.

The problem is not new anyway – I found a reference from The Oil & Colour Trades Journal of 1914 .. quote “An instance I came across some time back was of some [brunswick green] being painted on corrugated iron and turning blue. This I put down to the action of the sun causing the chrome to fade and leaving the blue.”

The author goes on to state that Brunswick greens usually darken – an observation repeated elsewhere in the case of paintings exposed to light – this makes me think that exposure to water is necessary for the bluing effect.

I also enjoyed your post on ‘invisible green’ by the way – I’ve come across this term once before – as it was used as the colour for the liveries of the locomotives of the Hull and Barnsley Railway – according to the literature this particular invisible green was so named because it appeared completely black, except in the brightest sunlight – under which it took on a slightly green tint – the recipe for this pariticular version was a 50:50 mixture of drop black and brunswick green.

PatrickNo Gravatar » 30. Jun, 2013

Thank you for adding so much to our understanding of this phenomenon.

Jennifer HallidayNo Gravatar » 24. May, 2015

Patrick, we have just returned from a tour of some National trust properties and were admiring the exterior paint colours, specifically at Hidcote Manor. Can you help with colour names, suppliers etc. I live in Australia. Jennifer