Bimetallic Cats

Bimetallic cats

Photo via Thank you and thanks as well to Lesley Morgan.

The description bimetallic cats refers to a unique coat coloration. Bimetallic cats are flesh and blood not metal. The term currently relates mainly to Siberian cats, which are a pedigree cat that looks like a Maine Coon or Norwegian Forest Cat. All three may have the same ancestors. However, I think there are lots of random bred cats that are also bimetallic. At least they look it. Perhaps there has been little focus on moggies or perhaps I am wrong and Sarah Hartwell will scold me for writing that ;).

I am informed by Sarah Hartwell (thanks Sarah) that within some SIberian cat breeding programmes (lines) cats are popping up that have a golden-like “stain” of colour that appears to be laid over the existing tabby coat. When the tabby is a silver tabby, the effect is silver contrasted with gold, hence bimetallic Siberian cats. “Bimetallic” means two metals.

On certain occasions when the coat is suitable, adding golden blobs of colour can make the cat look like a tortoiseshell cat. Because tortoiseshell cats are almost always female, when a lot of male tortoiseshells turned up someone scratched their heads and asked questions.

It has now been decided that the bimetallic coat is due to a genetic mutation that was perhaps introduced into Siberian cat lines by a random bred (freeborn) foundation cat with which the pedigree cats were outcrossed perhaps to avoid inbreeding while improving the cat’s appearance.

What I mean by a “random bred foundation cat” is that all Siberian cats, Maine Coon cats and Norwegian Forest Cats are refined versions of the natural and original random bred cat (the moggie foundation cat) from Northeastern Europe and Russia (I suppose).

Within the current population of original Siberian cats there appears to be mutated gene that found its way to the cat fancy in America. I am not sure if the gene is recessive or dominant. I don’t think the experts know for sure but it seems to be a recessive gene brought out through line breeding. Recessive genes are often hidden and have no effect on the cat.

Here is photo of Lexus, a bi-metal Siberian cat of 11 weeks of age, from Facebook:

Bimetallic Siberian Kitten

Bimetallic Siberian Kitten

Below is a photo of a random bred tabby cat on Flickr. It looks to me like he is a bimetallic cat but no doubt there is some reason why he is not. Perhaps this is an example of rufinism, which is described as “the degree of expression of orange/yellow pigment”³.

Bimetallic cat

Bimetallic cat?

With respect to bimetallic cats, the genetic effect called “rufism” (also called “rufinism”) has been ruled out because of the “degree and intensity” of the colour¹.

At the level of each hair strand the golden colour is due to a broader band of phaeomelanin which is yellow/red/orange pigment in the hair strands. Melanin (eumelanin) is dark brown and the other banded pigment. This how a classic tabby hair strand might appear:

Tabby Hair Srand

Tabby Hair Srand

If the phaeomelanin band is wider the hair will look more orange/yellow hence the golden colour of these bimetallic cats.

Refs:  (1) (2) Original photo of tabby random bred cat on Flickr (3) Robinson’s Genetics 4th edition.

Facebook Comments


Bimetallic Cats — 13 Comments

  1. Pepi – the one who vanished one day – looked exactly as the tabby in the lowest picture. Almost like caramel colour. I clearly remember that about him.

    • I am hoping for a comment from Sarah Hartwell. She’s the expert. Even the experts are learning about cat genetics and most of what they learn is about breeding (appearance). I think it is fair to state that. The other area is health – picking out the genes that cause inherited health problems. I guess you haven’t got a picture of Pepi have you?

  2. All the bimetallics originate from Polish lines. So far they’ve turned up in Aus, Germany, Poland and the Netherlands (not in the USA as far as I know). They could be linked with a dynasty of non-silver Siberian cats that presented as fertile torbie males. It’s still under investigation. There’s now a group of breeders getting together to investigate further.

    • Thanks Sarah and thanks for talking to me about it. It is an interesting subject in the cat world. Of course outsiders will think we’re a bit crazy…but we’re not.


    In the 1980s, a phenomenon was seen in some American lines of shaded silver and chinchilla Persians. In adulthood, the cats developed cream or golden patches and finally changed completely from silver to a pale golden colour. At first, this was dismissed as “tarnish” caused by the silver gene being incompletely dominant so that a yellowish colour “broke through”. It became apparent that the change to golden was progressive, starting on the cat’s back and spreading. All affected cats could be traced back to a 1950s stud whose male progeny were influential studs in North America. The effect was informally dubbed “platinum”.

    Next to attract attention were the “X Colour” Norwegian Forest Cats. Black or blue (self/solid, tabby or silver tabby etc) Norwegian Forest Cats changed in adulthood to golden and light golden colours. The change began on the back and spread from there. In self black and self blue, they became amber and light amber and the underlying tabby pattern became visible. They also had dark noses, distinguishing them from known golden colours. This is formally known as “amber” and “light amber”.

    Effects similar to amber have since turned up in a brown mackerel tabby of Manx origin (born of an accidental mother-son mating) who is currently transforming from a black-marked brown tabby to a reddish-marked golden tabby. Similarly, “sorrel” (an informal term) Bengals are those where the pattern colour has faded from black to reddish brown.

    Another colour-change effect turned up in a line of New Zealand-bred Brown Burmese cats and Mandalays (a relative of the Burmese). Instead of turning golden from the spine downwards, they were born a lavender colour and progressed through lilac-caramel then chocolate ticked and finally russet (reddish ticked) with an ivory underside.

    The latest colour-changers (so far) are Siberians that developed golden patches. Although noticed in silver Siberians that have been informally dubbed “bimetallic” for their mix of silver and gold in the coat, the effect probably occurred in some years earlier in brown tabby Siberians that resembled torbie cats … but were male. In bimetallic cats, the initial red or golden patches are often on the back of the neck and may spread randomly through the coat.

    What do these all have in common? They all appear to be the result of an “extension gene” a.k.a “red factor” (also known in cats as “black modifier” or “late colour change” gene) that controls the production of red and black pigment. The dominant form of the gene produces black pigment, while the recessive “non-extension” form produces a red pigment. The name “extension” comes from the effect of the black or brown colour being restricted to the skin of the extremities (e.g. the nose leather in amber Norwegian Forest Cats) and not extending to the rest of the body. The extension gene is responsible for the bay colour of horses. In Norwegian Forest Cats, amber is due to a mutation of the MC1R gene.

    It’s not just domestic cats that can have this effect. A similar effect has been seen in leopards where it converts spotted leopards into red-spotted “strawberry” leopards, while black leopards become mahogany-coloured with darker brown spots.

    • Hi Tamara. He does look as if he could be bimetallic, yes. I have darkened your photo a bit and marked up where I think the golden overlay is. Thanks for showing us. Very handsome cat.

  4. Thanks. Yes, your edit actually looks a little more like him. Here is his belly from about two months ago. His coloring was more silver when he was even younger.

    He’s much much longer now, and weighs almost eight pounds at five and a half months.

    • Nice photo Tamara. All fur and fluff with little patches of gold. Sarah Hartwell is the only person I know who could adjudicate on whether he is bimetallic. She is the expert. Bimetallic cats are a new discovery so there will only be a few people who know much about them. Thanks for the second photo.

  5. I am posting this on behalf of Nina:

    I suppose this is a bimetallic housecat, she is blue tabby, on her back she is silver shaded (2/3 of her fur are white, tips are blue/blues striped) an her belly is golden shaded. We don’t know who were her parents, in shelter they said her mother was “whiskas-like” housecat and father was probably british shorthair.

    bimetallic cat

Leave a Reply

Your email address will not be published. Required fields are marked *

Please only upload photos that are small in size of max 500px width and 50 KB size. Large images typical of most default settings on digital cameras may fail to upload. Thanks.