Alchemy is not about transmuting materials to gold. It is not about chemistry. It is not about magic.
Alchemy is way of life. That's right. It is a ideology. A religion. And as every religion has it goal, to become perfection, to be resurrected, or to accomplish nirvana, in the same way alchemy has it's goal to accomplish perfection. In that time gold was treated like perfect metal. So alchemists wanted to make other metals into gold to make them perfect, but that was not even close to the core of alchemy, as I said it is the way of life.
Alchemists never, NEVER, managed to accomplished their goal. They NEVER transmuted other material into gold. That was their search for holy grail, that they never accomplished. In the history there were many forgers, that made chemical processes modern chemistry knows about to make some metals look like gold, nothing special, but they earned for their living. So forgery was about making other metal looks like gold, not alchemy. It is true modern chemistry can be very grateful to alchemy, but alchemists never meant to make such breakthroughs, they were only interested in their philosophy and perfection. A digression if you like. You respect Isaac Newton, right? He is a great physicist in your eyes, isn't he? A hell he is. He was alchemist. That was his life. All things he made for physics he made by the way while he deliberating about he's life - alchemy. So no one can say alchemy is bullshit, because it meant much to the world's progress.
And someone mentioned magic? Yes, some alchemists practiced magic. Magic then was popular like quantum physics is today. So they tried all methods they knew to reach perfection.
And Soul (member, not term), only thing why we can make synthetic diamonds from coal is because they are made from same element - carbon. Diamond is allotropic modification of carbon. For instance, graphite is also allotropic modification of carbon. Such different materials and they have same atoms, interesting, isn't it? But they have different structure (bond between atoms). So what scientist made was changing structure of an element. To make gold from some other element, we would need, not only change structure, but to add protons, neutrons and electrons to that metal. And I think, under condition we have technology for such thing, it would be very unprofitable. So, for current time being we can't even dream about it. I believe it will be possible one day (but also believe we will kill each others including destroying our planet before we make such breakthrough).