The chemistry behind arts


Before the industrial revolution in the 19th century, the range of colours available for paintings was rather limited. Only naturally occuring earth pigments, minerals and some materials of biologic origin, for example insects, could be used.

While earth pigments like ochre and other iron oxides have been since the stone age, other colours were much more difficult to obtain. They had to be traded over long distances during the middle ages and the renaissance. Some colours like blue and purple were especially expensive and became associated with royalty. In the 18th century, the first cheaper, synthetic colours, for example Prussian blue and Scheele’s green, were invented which made them more accessible to artists.

These colours normally came in powder form and when an artist got a hold of the pigments he needed they still had to be mixed with a liquid. For oil paintings, the powders were normally mixed with linseed oil forming a paste which had to be used right away. Other painting techniques preferred other liquids, for example water was mixed with colour pigments to create watercolor paintings called ”aquarelle” in French. This technique is still very common in school art lessons today.

Let us go through different colours and look at how they have been produced throughout history. You can even find the information in the infographic above.

Red – This colour can be created with iron(III) oxide which has been used since the cave paintings of the stone age. During the Roman Empire and the middle ages, another red pigment called ”minium” with the chemical name lead(II,IV) oxide became popular, especially to colour manuscripts. Lead-containing substances like minium are poisonous and small amounts are accumulated in the body during permanet exposure. This shows that not all the colours used by artists throughout history were safe and we will encounter even more toxic pigments further on. Fortunately, a non-toxic red pigment came into use during the 16th century. It consisted of the dried, pulverized bodies of female cochineal bugs from Southern America. This pigment is still used today, for example in lipstick colours.

Yellow – Also yellow pigments have been around since the stone age. They were produced from ochre, which has the chemical name hydrated iron oxide. In 1797, the synthetic pigment chrome yellow, also called lead(II) chromate, was invented by mixing solutions of lead nitrate and potassium chromate. It became popular among artists during the first half of the 19th century. Due to the contained lead and chromium this pigment was poisonous as well.

Blue – Before the 18th century the main source of blue pigments was a semi-precious stone called ”lapis lazuli” which could only be found in one mountain range in Afghanistan. This is the main reason for its high price and the difficulty to obtain blue colours. The situation changed in 1704 when Prussian blue was invented as a cheaper, synthestic pigment. Prussian blue refers to range of compounds that are made up from iron, carbon and nitrogen. Carbon and nitrogen are joint together as cyanide ions that form so-called coordination complexes with iron in the center. Despite the presence of cyanide ions, these pigments are non-toxic and still in use today.

Green – Originally, the mineral malachite with the chemical name copper carbonate hydroxide has been employed as green pigments. In 1775, the Swedish chemist Carl Wilhelm Scheele invented a substance called copper arsenite which became a popular pigment under the name Scheele’s green. You might have guessed it from the chemical name, this compound contained arsenic which made it very toxic. Among all the poisonous colouring agents that have been used throughout history, this was probably the most lethal one. Especially its use in wall paper and clothing has been linked to many deaths during the 19th century in Britain and Europe.

Violet – Traditionally, mixtures of red and blue were used to create violet. The difficulty in obtaining blue colours made violet very expensive as well. During the 19th century, the first synthetic, cheaper pigment called manganese violet became available. Its chemical name is ammonium manganese(III) pyrophosphate and it is still used in cosmetics such as makeup and hair colouring.

White – For a long time, a compound called lead carbonate hydroxide or white lead was used to produce white colours for paintings. But just like lead(II,IV) oxide (minium), its use is banned today due to the toxicity caused by the contained lead. The white pigment most commonly employed now in paints is titanium(IV) oxide.

Black – Just like red and yellow, black pigments have been around since the stone age and quite easy to make. The earliest black pigment was probably charcoal produced by burning wood or other vegetation. A popular method to create black pigments during the 17th and 18th century was burning animal bones in air-free chambers which resulted in pigments referred to as ”bone black”.

The chemistry of soaps and why it matters

Soap is made via a chemical reaction between a fat and sodium hydroxide (NaOH). The reaction is called saponification and produces salts which consist of sodium ions and fatty-acid ions. The latter have one long chain of carbon atoms each. These sodium-ion fatty-acid salts are very good at removing dirt and we also call them soaps. Their secret is that the non-polar, long carbon chains of the fatty acids are aranged in spheres around the non-polar dirt particles. The opposite chain ends, where the polar sodium ions are attached, face the polar water. These arrangements are called micelles and they can dissolve dirt from your clothes or skin.

Making soap in this way is actually quite environmentally friendly. Sodium hydroxide is normally used in the form of lye which is made by leaching wood ashes with water. Historically, the fat has often come from animals, but today fats from plants, such as olive oil or grapeseed oil, are used since they create nicer soaps. In summary, soap can today easily be produced using only renewable sources from plants.

Sounds like soap making is an eco-friendly process? Yes, but unfortunately reality looks very different. When I researched this topic, I was really shocked when I found out which substances are actually being put into these products, despite better knowledge.

Let us start by talking about the actual cleaning agents, the substances that remove the dirt. Traditionally, soaps as described above have been used for this task and I believed that this was still the case. But it turns out that today most cleaning agents are made from petroleum instead of vegetable oils. These petroleum-based chemicals work the same way as real soap does by forming micelles around dirt particles to dissolve them. They are, for example, found in laundry detergent and liquid body wash. Only bar soaps still contain the more environmentally benign, real soaps. But be careful, not all of them do. You should check if it actually says ”soap” on the packaging to be sure.

There are even more reasons why solid soap products are more environmentally friendly. On average the production of bar soap consumes five times less energy than liquid soap. Another important factor is water. Liquid soaps as well as liquid laundry detergents contain 80 % more water than their solid counterparts. In addition, liquid products come in non-reusable plastic bottles, while the solid products come in cardboard packaging.

Besides the petroleum-based cleaning agents, manufacturers often add a range of other questionable chemicals to liquid soaps. One famous example are parabens which are added to about 85 % of all liquid cosmetic products to prevent bacteria and fungus growth. Parabens can be mistaken for estrogen by the body which has been linked to both breast cancer and reproductive issues. It will be interesting to see if they could be related to the recently reported drop in sperm count among Western men. Also, paraben substitutes like phenoxy ethanol should be used with caution. Bar soaps and other solid cosmetic products, on the other hand, do not need any preservatives and are a healthier choice.

Some harmful chemicals could also be hiding under the label ”fragrance” or ”parfume”. Their compositions do not have to be revealed as they are considered trade secrets which leaves the consumer clueless about what they are made of. At least one villain chemical, called phthalates which has been linked to many health issues, is often included in parfumes as a preservative.

So, the bottom line is: use bar soaps, make sure that it contains real soap and check that all contents are revealed. As for laundry detergent, washing powder is better than liquid detergent. You can also easily make your own laundry detergent and bar soaps at home.


How does breathing change wine?

It is this time of year where you can sit outside in the evenings to hang out with friends. Throughout this time many bottles of wine are shared and enjoyed. During such an evening with several bottles of red wine, me and some friends noticed that the taste of one particular red wine became better the later the evening got. This was not because we were getting more and more drunk, but rather due to a process called ”breathing” or ”aeration”.

Breathing refers to chemical reactions taking place between the wine and the oxygen in air that start once the bottle is opened. Generally, two processes occur during breathing, these are evaporation and oxidation which cause the wine to release new aromas and flavors.

Evaporation is the transition from the liquid to the gas phase and some volatile compounds easily evaporate in contact with air. Examples are sulphur containing substances formed by sulphites in the wine. Sulphites are added to wine to protect it from bacteria. The second process, oxidation, is in this case the reaction of wine compounds with the oxygen in air, a similar process to the rusting of iron  (where iron reacts with the oxygen in air). Substances in wine sensitive to oxidation are various poly-aromatic compounds like catechins and anthocyanins. They are the flavor-rich, dark pigment molecules that give red whine its color.

It is worth mentioning that the production of flavor-rich, dark pigment molecules like anthocyanins and other poly-aromatic compounds in grapes stops at temperatures that remain constantly around 30 degrees Celsuis. This leads to a decrease of flavor-rich compounds and is one of many reasons why climate change is threatening to ruin the global wine production.

Additionally, ethanol, in other words alcohol, is sensitive to oxidation as well if a wine bottle is opened too long, for example over several days. During the oxidation of alcohol acetaldehyde and acetic acid are formed. Acetic acid is the main compound in vinegar and the reason wine turns sour after having been opened too long.

The last example shows that unlimited breathing is not good for wine either. In addition, not all wines benefit from breathing. Especially, older wines can deteriorate very quickly when in contact with air. Young, red wines, on the other hand, like the one my friends and me had, benefit a lot from breathing. White wines normally lack the dark pigment molecules that change during oxidation. For this reason breathing does mostly not alter the taste or white wines.

So, how long do you need to let a red wine breathe? Generally, you should taste a wine before deciding if it needs breathing at all. As bottle necks are quite narrow, they do not provide a lot of contact with air and the wine will need at least 30 to 60 minutes to breathe on its own. However, there are ways to speed up the process. For example, you could pour the wine into a decanter, a vessel with a neck for pouring and a very broad bottle body to provide a large surface area for the wine to breathe. You could also pour the wine back and forth between two vessels or just swirl your glass before drinking the wine.

I hope the weather is nice were you are, so you can enjoy a glass outside with friends tonight.