Even though I prefer to analyse linseed paint in its historic context and setting because there are at least a few centuries to work with, that doesn’t mean that I shy away from modern methods and techniques to gain a greater understanding.
Over the last 18 months or so, we have been working closely with the University of Bradford utilising their Project Cayman on getting a greater understanding of the make-up and working of linseed oil and linseed paint through spectroscopy, namely Scanning Electron Microscopy (SEM) and SEM-EDX (where the EDX stands for Energy-Dispersive X-ray). They are slightly different ways of getting a full particle breakdown of linseed oil and linseed paint with various pigments. It is exactly this powerful combination with a centuries old track record and modern methodology which gains such great insight. The focus of our analysis is to get an understanding of the molecular structure and build-up of the individual components of linseed oil and linseed paint. The main aim of this is to get a greater understanding why some products work better than others and how we can optimise their performance. Let’s start with having a look at the ingredient it all starts with, our Raw Linseed Oil. This image shows what it looks like under the SEM:
Figure 1: Electron Image of Raw Linseed Oil
Which translates into this graph:
Figure 2: Spectrum of Raw Linseed Oil
As you can see, it is all carbon and oxygen, showing no impurities.
It is essential for efficacy and drying properties to get the ‘cleanest’ raw materials to start with. Any impurities at this stage will only have greater impact further down the line. This is one of the reasons why the starting point for high-quality linseed paint should always be cold-pressed raw linseed oil. We get ours from a local farm so we can control the whole process.
Our linseed paint is made from boiled linseed oil and we use powder pigments to get the optimum efficacy and durability for the paint. Each pigment has a different profile though, and, therefore can perform a different function.
Iron Oxide haematite (fig. 3) clearly looks completely different from Graphite (fig. 4).
Figure 3 Iron Oxide haematite Figure 4 Graphite
We then went on to interrogate this further by means of ICP-MS. The acronym stands for inductively coupled plasma mass spectrometry. Mass spectroscopy is the analytical technique used to determine the (m/Q) mass-to-charge ratio of ions (identifying the mass and electrical charge of a particle). It is simply the method by which this is tested, in this case plasma heated by induction.
In very simple terms, this gives a ‘fingerprint’ of the chemical identity of the various components of a product. For our analysis, it is used to identify mainly the esters and any metal ingredients, as well as their ratios. It also helps in assessing the most effective environmentally and healthy dryers. In this case, the analysis shows the Calcium dryer we use.
Firstly, through Mass Chromatograms, we analyse the fatty acid content of various (raw and boiled) linseed oils. The main reason for this is that the purer the ingredients, the more stable and long-lasting the paint and oil is. The odd one out in this is pine tar (oil), which has a far higher complexity, as evident from Sample 7 (fig 5) which is worthy of a separate article.
Figure 5 Mass Chromatographs of various oils
Figure 6 Calcium dryer present in our linseed paint
What do other paints and oils in the market contain? Doing this exercise for various other linseed paint and oil in the market, it shows a huge range of dryers used.
Without naming names, it is clear that not all products offered are particularly healthy, as this table shows. The highlighted cells show our paint (Sample A – Prep 1) compared to another linseed paint brand (Sample 3 – Prep 2). As you can see, the titanium content is twice as high, and Manganese is almost off the scale. The use of heavy metals is not good for people using or mining it and leaves a big impact on the environment.
Figure 7 Analytical results for dryers
All this information informs us not just on how the various ingredients interact and what their efficacy is, it also helps us develop and improve the product further. Real powder pigments, rather than colourants actually have differing properties and can, therefore, perform different functions.
For instance, zinc white has a completely different profile from iron oxide and graphite. Understanding their make-up and role helps us mix and specify the correct product for specific purposes.
This does not mean we will be adding any petrochemically-derived ingredients, but more so that it gives us the option to experiments with various compositions and ratios of existing historic and naturally occurring ingredients. As always in science, there is no definitive answer, but I take great interest in all of this and will keep working on it.