In the journal “Chemistry and Life” No. 3, 1972, there was an article on how to grow crystals of metallic copper, it was well written and I will not retell it, I’ll just quote it:
LET'S GROW COPPER CRYSTALS
No, we didn't make a mistake. Not copper sulfate—you’ve probably received these crystals more than once—but real metallic copper.
You also apparently observed very small crystals of copper - they cover an iron nail dipped in a solution of copper sulfate. They are so small that the reddish film appears continuous and even. And in order to grow large crystals, you need to do this: slow down the reaction. When the molecules of the released substance are deposited onto ready-made small crystals, they will grow.
Let's do this. Place crystals of copper sulfate at the bottom of a jar or beaker, cover them with fine table salt and cover with a circle of filter paper or blotter, cut exactly to the diameter of the vessel. On the paper circle we will place a slightly smaller circle, this time an iron one. It needs to be cleaned with fine sandpaper. And finally, fill everything with a saturated solution of table salt so that it is several centimeters above the iron circle.Of course, you understand why table salt is needed. Absolutely right - to slow down the release of copper.
The preparation is completed, the experience itself begins. He will go without our intervention, we just have to wait and watch. How long to wait depends on the experimental conditions, primarily on the temperature. Usually, within a few days, shiny copper crystals will form. Their shape and size may vary depending on the size of the copper sulfate crystals and their quantity, the diameter of the vessel, the height of the salt layer, and temperature. Sometimes beautiful copper “trees” grow - dendrites (the word comes from the Greek “tree”), crystals that are not yet fully developed. Snowflakes, frost, frosty patterns on glass are also dendrites.
Of course, you will want to keep the crystals you receive. Rinse them with water, fill them with diluted sulfuric acid and keep them in a closed container, without access to air.
I. Ilyin.
The thicker the layer of table salt and the lower the temperature, the slower and, therefore, the larger and more shaped the crystals will grow. Also, the size of the crystals and the growth rate will depend on the size of the crystals of table salt, since the crystals grow in the layer of salt, between its crystals. Table salt and copper sulfate are cheap and readily available compounds, and it seems to me that it will be very interesting to conduct research in order to identify optimal growth conditions and obtain correct and large crystals.
