While amalgam gilding on iron/steel did indeed exist in Europe prior to the 19thC, its use was primarily applied, to decorative objects which would not be subject to wear. Prior to the 1800s the gilding of swords and armour in Europe was almost exclusively performed with foil using Numone-Zogan like technique, or a heat/burnishing method. The damascening (Numone-Zogan) technique produced the most lustrous and long wearing of all three. Amalgam gilding, in the realm of weapons was essentially limited to the gilded highlights of the blued first third of post-1740 blades, which received adequate protection from their scabbards, and thus did not require the more elaborate and time consuming techniques.
The Technical Encyclopedia referenced below describes the three methods. You may be interested to learn that the amalgam gilding of iron/steel did not necessarily require prior copper plating. I've included a 'google translation' of the relevant section for those among us who might find it laborious to wade though 18thC French texts.
Hope this is of interest,
Encyclopédie méthodique. Arts et métiers mécaniques. Tome 2 / , [par Jacques Lacombe] - 1782-1791 p 352-354
"Gilding on fire or on metals.
There are three usual ways of gilding with fire, to know in ground gold; in gold simply in foil, and in chopped gold; but we can add a fourth, which we will discuss at the end of this article. Gold gilding or gold vermeil, is made with gold amalgamated with mercury, to a certain extent, which is usually an ounce of quicksilver on a big gold.
For this operation the crucible is first blushed; then the gold and the quicksilver having been put in it, they are gently stirred with a hook, till we see that the gold is melted, & incorporated into quicksilver; after which they are thus thrown together in water to wash them. To prepare the metal to receive the gold it is necessary to clean the metal that one wants to brown; what is done with strong water weakened with water; this is called pickling or stripping. The metal being well dried, it is covered with this mixture of gold and bright silver, extending it as much as possible; in this state the metal is set on fire on the grate, or in the basket to be gilded, above which is a stove full of fire. The grate to be gilded is a small lattice of trellis thread, of which the pan is covered, and on which the work is laid; those that are silvered do not need so much cleanliness. The basket to be gilded is also a lattice of wire, which differs from the grid only in that it is concave & pressed a few inches. As quicksilver evaporates, if. that we can distinguish the places where it lacks gold, we repair the work by adding new amalgam where it is needed. To make this gilding more durable, the gilders rub the work with mercury & etching, and gild a fertilized time in the same way. They sometimes repeated this operation up to three or four times for the gold covering the metal to be of a suitable thickness. When the work is in this state it is finished with the brush-scratch which is a brush made of small brass threads. Lastly, it is colored by a process of which the gilders make a secret, but which is probably the same as that used to give color to the species of gold, which is described by the word Monnoyeur in the article on Le Blanchiment.
To prepare the metals to receive the gold leaf gilding, one begins by scratching them with the grating, which is a sharp iron with four sharp edges similar to the iron of a sting. It is two to three inches long, and has a handle twelve to fifteen inches long. When the metal has been well scraped it is po! It with the sharp iron polisher, which does not differ from the burnisher of which we spoke above. Then the metal is heated. This operation is called blue, because when it is done on iron, it takes a blue color.
When the metal is hot enough, apply the first layer of gold leaf that is slightly cleaned with a burnisher or polisher. The action of swallowing is to press against the forceps with this instrument, the leaves that have been applied. Normally only three or four layers are given, of a thin sheet of gold in the common works, and of two leaves in the fine works, and at each layer they are cut down and then put back into the fire, which is called annealing. After the last coat, the gold is able to be light brown with the burnisher of sanguine also called stone to brown.
Gilding, which is called chopped gold, is done with gold leaves like the preceding, and it is practiced in the same manner, but it differs in two essential points.
1. When the metal has been scraped & polished, a prodigious number of small hatches are made, in all directions, with the chopping knife, which is a small knife with a short and wide steel blade, fitted with wood or wood. horn. These make the hatching made on the metals before the gold is applied to it, which have been called the chopped gold gilding, although the hatching no longer appears on the outside, when the gilding is finished.
2. For minced gilding it takes up to ten or twelve layers, two sheets of gold for each layer, instead of three or four for plain gilding. This large quantity of gold is necessary to cover the hatching, but the gilding, which is then much more beautiful and more solid."