I've read in some book that one of the old chemists was able to transform cheap metals into gold.
I know that gold is an element (Au) so we can't transform a metal into Au. But as I read further it says that the chemist doesn't actually transform metals into gold but into something very similar to gold (similar physical and chemical characteristics ) such that you can't differentiate between it and between gold.
Is this chemically possible?
In the days before chemistry, alchemists searched for the Philosopher's stone which would enable them to transform base metals into gold. They spent a lot of effort searching for it but we know now that their search was futile as no chemical process can cause elemental transformation. Only nuclear processes can do that but they cost far, far more than mining the element ever will so this doesn't really count as a solution.
But plenty of people faked a result or were conned by their lack of understanding. Fool's gold, for example looks a lot like gold, but doesn't share many other properties but, presumably, the name arises because some people are gullible. There are also many metal alloys that look like gold but are not pure (including many alloys that contain some, but not much, gold). It is also possible to use a variety of chemical or electrochemical processes to coat the surface of many metals with a thin film of gold.
But careful analysis can reveal most of these methods of fakery (including the alloying of gold with other metals which was very tempting when coins were made of gold). One of the most famous stories of Greek science is based on one of the most reliable methods. Archimedes was faced with the task of distinguishing debased coinage or other gold objects and, in the legend, realised the answer while having a bath, leapt out the bath and ran down the street naked yelling "eureka". What he realised was that an object immersed in water displaces a volume of water equal to its volume and this can be measured by weighing the displaced fluid. Combined with the weight of the object this can be used to estimate the density of the object. Since the only other metal with a density close to gold is tungsten (gold is 19.28 g/cm3 and tungsten is 19.25 g/cm3) knowing the density is a good way to test the purity of the metal. Common metals used in alloys, like silver (density 10.5 g/cm3) will substantially lower the density.
So, in short, you can make a lot of things that look like gold, but it is very hard to make something that shares enough properties to convince a skeptical observer who will test more than the appearance.
No alchemist can perform transmutation of lead into gold with alembic! But now day we can perform nuclear transmutation and gold can be now synthesized by irradiation of mercury or platinum in a nuclear reactor or with an accelerator. However this is not cost effective!
In fact there are many alloys that looks like gold and an alchemist could make easily most of them. Brass is one metal that can be similar to gold varying the copper zinc ratio you can make Aich's alloy and Prince's metal two types of brass with an aspect very similar to gold. In ancient rome aurichalcum was a metal (brass type alloy probably) with an aspect similar to gold. The problem is that usually you don't see if something is made of gold you feel it! If you try to cheat someone who deal with gold with these metals he suddenly tell you that they are to light to be gold! Gold is in fact heavier than lead! This is why density esteem works great and simply coating the surface with gold doesn't work. Ethiopian fake gold fail for that!
So to make a good gold sophistication you have to find an isobar of gold, an element with the same weight and density of gold. Tungsten is a perfect candidate, and sometimes you can read about founding of gold plated tungsten bars or other theory about FortKnox. Here you can read a good article about gold sophistication. In this case a layer of gold over the tungsten is needed to make it looks like gold and to pass the exams with superficial elemental analysis.
For a good looking gold surface I prefer iron(III) oxide mica pigments very nice color without cheating nobody!
