How can metals smell of something?

Imagine the smell of silk, chalk or plastic. You could attach attributes to these notes – usually by association, but bear in mind that these scents would be synthetic reformulations of naturally-occurring organic and inorganic compounds. Mineral notes, for instance, includes Asphalt, Asphalt accord, Black ink, Black kyanite [Kyanite is a typically blue silicate mineral], Black tourmaline [Tourmaline is a crystalline boron silicate mineral], Blue kyanite, Brine-coated wood, Burning stone and Chalk. But these terms are dense with implications. What makes it possible to smell something that has no smell? How can perfumers include ingredients in their perfumes that are involatile (stable) or inorganic?

“To perceive a smell it has to be volatile; molecules have to physically fly into your nose, come into contact with a receptor and launch a chain of biochemical processes that the brain interprets as a certain type of odor. But it does not seem that metals are excessively volatile, with the exception of mercury. Besides that, smell is a characteristic of substances with a molecular structure, but substances with an ionic lattice (for example, inorganic salts) or a metallic lattice (iron) should not smell.” (Metallic Scent In Perfumery by Matvey Yudov)

Therefore, the only way we can smell things like coins, door handles, cutlery, keys or even chalk, is if they come into contact with human skin. Our skin perspires, and chemically, the perspiration is mostly fat and fatty acids.

“The main cause of a metallic smell is hidden in fats, which are oxidized under the impact of oxidoreductases (a group of enzymes which catalyze the transfer of electrons from one molecule to another, which is called oxidation for losing electrons, and reduction for gaining them). Iron cations Fe2+ decompose lipid peroxides, producing intensively smelling substances. Only a small amount of iron ions is needed to produce such an amount of volatile substances which we are able to smell. For the same reason, blood has a characteristic metallic smell; iron contained in hemoglobin launches a similar reaction. […] These reactions are reproduced in the laboratory to create metallic-smelling substances. Substances which cause a metallic smell are usually unsaturated aldehydes and ketones.

1-Octen-3-ol_Formula

One of them, oct-1-en-3-one, or amyl vinyl ketone, you can meet in the perfume lab. In its pure form, it has an earthy metallic smell with mushroom and vegetable nuances, and some kind of fishy note, a similar smell you sense while preparing freshly caught sweet water fish.” (Ref. Matvey Yudov)

“Black Vinyl” – taking apart A synthetic scent

Hemlock, designed by Parfums Quartana, with perfumer Christelle Laprade.

One synthetic-sounding component is “black vinyl accord”, or just “black vinyl”. This is one of the many ingredients in Hemlock, by Joseph Quartana and perfumer Christelle Laprade. Hemlock is part of Parfums Quartana’s debut collection, Les Potions Fatales. Black vinyl is said to smell like a combination of metal, plastic, blood, and mushrooms. And it is just one of its many notes.

The “vinyl” element is itself an “accord”, a blend of notes that, together make up a new, different note. One of the (many) notes in this accord is mushroom-smelling, and actually naturally-occurring substance called amyl vinyl carbinol – which explains one of the notes in the accord, but not all of the notes in the perfume. Altogether, this is a very complicated formulation.

“In perfumery, terms like “black vinyl” are made up so it has no precise definition. To my imagination it would smell like sweet-plastic. i.e. slightly chemical but with a richness to it like vinyl plastic would suggest. The term vinyl [amyl vinyl carbinol, also known as 1-Octen-3-ol a.k.a Octenol] in the chemical name of this compound only suggests a part of the structure [or the “accord”], in the same way in which a brick is a part of a house, and the house is totally different to the brick. The odour of amyl vinyl carbinol is completely mushroom. Take a brown mushroom and put it to your nose, that is essentially the smell, very “’shroomy”, earthy and fungal. Something you would put in a stew. “

[This one sub-component, amyl vinyl carbinol] is found in nature and would be used as a top note modifier in perfumes, where, given its potency and peculiar odour type, it can work wonders or havoc depending on the formulation. This compound can be used to create either a natural effect in a perfume or a signature odour if blended with the correct modifier. It is not easy to use.” – Analysis by Max Millies, Earthgro Fragrances

Minerals and metals on the fragrance wheel

While many fragrance wheels or listings of fragrance notes include inorganic and synthetic ingredients,  a name or descriptive term is often not what is seems. Below is a variation, from Fragantica, on the classical “fragrance wheel” which acts as a standard reference point for perfume notes. Note that they have included earthy notes, mineral notes and textile notes.

       
Note category Examples Note Category Examples
Aldehydes ✱✱Aldehydes are organic, not only synthetic, compounds present in various natural materials
for instance natural citrus essences, pine essence, and cinnamon bark.
Amber notes ✱Natural  – originally aromatic tree resins, nowadays a combination of benzoin, labdanum, and vanilla, or else a chypre with a tonka-bean base instead of vanilla.
Animalic notes ✱Natural – For instance civet, skin and leather Aquatic notes ✱✱For instance algae, driftwood, sea water and ozone
Balsamic notes ✱Natural – From balsam Citric notes ✱Natural
Earthy notes ✱✱✱For instance peat and sand Floral notes ✱Natural
Fruity notes ✱Natural Gourmand notes ✱✱For instance coffee, chocolate, liquorice and mushrooms
Grain notes ✱Natural Green notes ✱Natural
Herbaceous notes ✱Natural Mineral notes ✱✱✱For instance gunpowder, salty notes, ink, sand, plastic/vinyl
Mossy notes ✱Natural Musk notes ✱Natural
Unclassified notes ✱✱For instance  carrot, datura (poisonous vespertine flowering plants), and hamamelis (witch hazel) Oriental notes ✱Natural
Powdery notes ✱Natural Resinous notes ✱✱✱For instance beeswax, “dragon’s blood”, and storax (or styrax/liquidambar)
Smoky notes ✱NaturalFrankincense and Egyptian Khyphi (incense) Spicy notes ✱Natural
Textile notes ✱✱✱For instance cotton, Linen, Silk, Velvet, Wool, Tobacco notes ✱Natural
Woody notes ✱Natural

Natural – Meaning it is originally occurring in nature – can be cloned or recreated in a laboratory
✱✱ – Meaning it can be synthetic, or cloned“cloned from nature” / “nature identical compound”, or both synthetic and natural
✱✱✱ – Unknown


Header image: Photo by John Sullivan, CC0 License, ✓ Free for personal and commercial use
✓ No attribution required. Source: https://www.pexels.com/photo/black-coupe-during-evening-166126/

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s