A Wee Bit Stroppy

Christopher Merrett
George Perfect Harding, (c.1820-50)

Antonio Neri's first translator was a London physician named Christopher Merrett. He was an early member of the Royal Society and completed several projects for them. Besides Neri's book, he compiled several volumes on flora, fauna and minerals. He published work on herbs and flowers, which was criticized as derivative, and he made some important contributions to the invention of carbonated wine (champagne). At the behest of physicist Robert Boyle, one of the founding members of the society, he spent considerable effort on the translation of L'Arte Vetraria into English in 1662. He sought out glassmakers, observed work in progress and tried, unsuccessfully, to find out something about the author himself. Nevertheless, he seems to have disliked Neri, or at least was very annoyed by him. Most notably, in the book, he complains about Neri's "nauseating repetitions" and decides to reorganize the structure of the volume. Dispensing with many of Neri's personal remarks, he congratulates himself on his "ingenious" changes to the text.

Merrett was also the first official librarian for the Royal College of Physicians. Through his dealings with them, we can see his ornery streak more clearly. In the 1666 great fire of London, the library and much of the college had burnt to the ground. He personally saved about a tenth of the 1300 volumes. Nevertheless, with the library, college and much of London gone, Merrett demanded his usual salary from the college and when they refused, he sued them in court. Later he got into a rather nasty public dispute with apothecaries over how to fill prescriptions. He was incensed at the practice of occasionally substituting unavailable ingredients for others that were at hand. In the end he was expelled from the College of Physicians, and to this day remains the only member ever to be banned for life. He retreated to his private practice and retired in obscurity.

Merrett's translation appeared a year after Neri's original was reprinted for the first time, in Florence, and a year before another edition printed in Venice. For the most part, Merrett's version of Neri is accurate, although he does go off the rails in a few places. He translates the Italian term for beadmaking "conteria" as “counting houses” rendering several passages completely nonsensical. As mentioned above, he decided to collect repetitious information at the beginning of sections, which does condense the text, but at the same time makes the book very difficult for any craftsman to actually use. On the other hand, he did introduce Neri's recipes to the English speaking world for the first time and he added extensive remarks and annotations, starting a tradition that would continue in later translations into French and German. The next translation after Merrett was into Latin, in Amsterdam in 1668. This version pays homage to Merrett but reverts to the original Italian for translation purposes, restoring Neri's format. 

The 1666 Great Fire of London
"Ludgate in Flames" (c. 1670)
Attrib. Unknown

Only fifty years after Neri’s death, Merrett stated that “Concerning our author, and this work, I find no other mention of him” (aside from two minor references). It is a shame that the physician did not have contacts in Florence, because he would have certainly found Neri’s nephew, living in the family palazzo on Borgo Pinti, practicing medicine himself. Antonio Neri was celebrated locally, in Italy; the Accademia della Crusca had adopted a number of his glassmaking terms for their groundbreaking dictionary. But it was Boyle and Merrett who put Neri on the path to greater notoriety throughout Europe. The book was translated and reprinted dozens of times, yet the life of the author remained largely a mystery. Neri was remembered briefly in the eighteenth century by Florentine historian Targioni-Tozzetti and again in the nineteenth century by Inghirami, Poggendorff, and in numerous short entries of other biographical dictionaries. By then, his book had become a classic text on glassmaking, yet still almost nothing of the author’s life was written. 

Regardless of Merrett’s difficulties with the College of Physicians, the apothecaries and his apparent dislike of Neri, it cannot be said that he was entirely humorless, even if on the dry side:

Glass is one of the fruits of the fire. Which is most true, for it is a thing wholly of Art, not of Nature, and not to be produced without strong fires. I have heard a singular Artist, merrily to this purpose say, that their profession would be the last in the world: for when God should consume with fire the Universe, that then all things therein would vitrifie and turn to glass. Which would be true upon supposition of a proportionable mixture of fit Salts, and Sand or Stone.

Ultramarine

Cappella Scrovegni (Arena Chapel), Padua
Frescos and ultramarine ceiling, Giotto 1306

In his fifteenth century handbook for painters, Cennino Cennini said, "Ultramarine blue is a color illustrious, beautiful and most perfect, beyond all other colors; one could not say anything about it, or do anything with it, that its quality would not still surpass." The ancient Egyptians used ultramarine to decorate the sarcophaguses of their pharos. Later, Marco Polo reported that it was made at a lapis lazuli mine in Afghanistan. Its name alludes to these far-flung origins: ultra-marine="beyond the sea." Venetians were probably the first in Italy to learn the extraction technique and import the raw lapis. Producing the rich blue pigment from the rock was no simple task; success required an elaborate set of steps. Because of the difficulty, for a time, an ounce of ultramarine was valued more highly than an ounce of pure gold. In the legal contracts drawn up for commissioned paintings, patrons often stipulated exact amounts of the precious material for the artist to use. Beyond its beauty, its presence in a painting signaled the wealth of its owner.

In the last part of his book, L'Arte Vetraria, Antonio Neri presents his recipes for a variety of paints, including one for ultramarine. In glassmaking, drinking goblets adorned with delicate paint-work raised their value and elevated them into the realm of art. Unlike enamels, which fired into the glass, most paint, including ultramarine could not survive the furnace, requiring application only after a piece was finished. The number of different paint and lake recipes in the book indicates Neri's familiarity with the craft. This, combined with his willingness to use other painter’s materials like "smalt" in his glass formulations, hints at a still unknown chapter in the alchemist's life. Perhaps, for a period in Antwerp, he worked directly with fine artists. Here is Neri’s ultramarine:

Take fragments of lapis lazuli, which you can find plentifully in Venice and at low prices. Get fragments that are nicely tinted a pretty celestial color and remove any poorly tinted fragments. Cull the nicely colored fragments into a pot and put it amongst hot coals to calcine. When they are inflamed throw them in fresh water and repeat this twice. Then grind them on a porphyry stone most impalpably to become like sifted grain flour. 

Take equal amounts, three ounces each, of pine pitch, black tar, mastic, new wax and turpentine, add one ounce each, of linseed oil and frankincense. I put these things in a clay bowl to warm on the fire until I see them dissolve and with a stirring rod, I mix and incorporate them thoroughly. This done, I throw them into fresh water, so they will combine into one mass for my needs. 

For every pound of finely powdered lapis lazuli, ground as described above, take ten ounces of the above gum cake. In a bowl over a slow fire, melt the gum, and when it is well-liquified throw into it, little by little, the finely powdered lapis lazuli. Incorporate it thoroughly into the paste with a stirring rod.

Cast the hot incorporated material into a vessel of fresh water and, with hands bathed in linseed oil, form a round cake, proportionately round and tall. You should make one or more other of these cakes from the quantity of the material. Then soak these cakes for fifteen days in a large vessel full of fresh water, changing the water every two days. In a kettle, you should boil clear common water and put the cakes in a well-cleaned, glazed earthen basin. Pour warm water over them and then leave them until the water has cooled.

Empty out the water and pour new warm water over them. When it has cooled, pour again, replenishing the warmth. Repeat this many times over, so that the cakes unbind from the heat of the water. Now add new warm water and you will see that the water will take on a celestial color. Decant the water into a clean glazed pan, pour new [warm] water over the cake and let it color [the water].

When it is colored, decant it and pass it through a sieve into a glazed basin. Pour warm water over the cake, repeatedly until it is no longer colored. Make sure that the water is not too hot, but only lukewarm because too much heat will cause the blue to darken, hence this warning, which is very important.

Pass all this colored water through a sieve into the basin. It still has the unctuosity of the gum, so leave it to stand and rest for twenty-four hours; all the color will go to the bottom. Then gently decant off the water with its unctuosity, pour clear water over it and pass it through a fine sieve into a clean basin.

Pass the fresh water through the sieve with the color stirred-up so that this color still passes through and therefore a great part of the filth and unctuosity will remain in the sieve. Wash the sieve well and with new water again pass the color through. Repeat these steps three times, which ordinarily leaves all the filth on the blue resting in the sieve. Always wash the sieve each time, cleaning it of all contamination. Put the blue in a clean pan. Gently decant off the water and then leave it to dry. You will have a most beautiful ultramarine, as I have made many times in Antwerp.

The amount per pound of lapis lazuli will vary. It depends on whether the lapis has more or less charge of color and on the beauty of its color. Grind it exceedingly fine on the porphyry stone, as described above and you will succeed beautifully. 

For a quite beautiful and sightly biadetto blue that mimics ultramarine blue, take ordinary blue enamel and grind it exceedingly fine over the porphyry stone, as above. Incorporate it into the gum cake with the dose described above and hold it in digestion in fresh water for fifteen days as with the lapis lazuli. Follow the directions for the lapis lazuli, in all and for all, until the end. These blues are not only useful to painters, but they also serve in order to tint glasses par excellence.

Faux Pearls

Johannes Vermeer
"Girl with a pearl earring" (1665-6)

Natural pearls, found inside various seashells, have been prized and worn as jewelry since antiquity. The pearl is formed as a secretion of the mollusk; it is the animal's response to an irritant, perhaps a sharp grain of sand, which has become lodged in its tissue. The secretion, called "nacre" is the same material from which the mollusk builds and enlarges its shell. Natural pearls are rare; large, well formed ones are even more so. A famous legend claims that Cleopatra used pearls to win a bet with Marc Antony: that she could spend ten million sesterces on a single meal. She literally drank pearls that had been ground up and dissolved in wine. Because of the difficulty in obtaining pearls, and their high demand among the wealthy, it is not surprising that like artificial gems, artificial pearls have enjoyed a brisk trade throughout history. 

In Antonio Neri's era, a number of recipes used glue, egg whites or other organic materials to simulate pearls. These had the obvious disadvantage of being susceptible to degradation by moisture and physical handling. Another alternative was to simulate pearls with glass, and on this count, Neri does not disappoint. Recipe number sixty in his book L'Arte Vetraria gives his prescription for artificial pearls. Here it is in its entirety:

 In fused and clarified cristallo, add three or four portions of tartar from wine dregs. You must thoroughly calcine this tartar to a white color. Stir it thoroughly into the glass, and continue to add more tartar, also well calcined until it is white. Add four to six more portions, always stirring the glass thoroughly, continuing thus until the cristallo takes on a pearl color. In this recipe, I cannot give exact rules, because it is a matter of experience, which is gained through experimentation. Once obtained, you must work the color quickly, because it will dissipate. I have practiced and experimented with this method many times.

"Cristallo" is the exceptionally clear glass the Venetians developed, perfected and were renowned for throughout Europe. "Tartar" is a crystalline growth that forms on the inside of wine casks, what we now know as "cream of tartar." Occasionally, one might spot crystals at the bottom of bottles of wine. They are a rich source of potassium. Neri, the Venetians and others had used tartar as a glass flux over a period of centuries. Here, however, he is not using it as a flux, but as a colorant to give the glass the pearl's shimmering appearance. His claim to making many batches of this glass implies large numbers of artificial pearls were in circulation. Our glassmaker presents a second recipe, which does not make any mention of pearls, but oddly may have much more to do with the evolution of reproducing these treasures of the sea. Recipe number 114 is entitled "The Way to Tint Glass Balls, and Others Vessels of Clear Glass, From the Inside, In All Kinds of Colors, So They Will Imitate Natural Stones." Here, Neri spreads fish-glue on the inside surface of a blown globe of clear glass, followed by various pigments.

Even in his time, artificial pearls found their way into royal courts and onto the canvasses of master painters. The fashion-setting monarchs of France and Britan, Catherine de' Medici and Elizabeth I were famous for their extravagant love of pearls. Elizabeth famously purchased faux pearls from Venetian glassmakers to adorn her garments. She commissioned many portraits donning her pearl studded creations. Referring to the famous painting by Johannes Vermeer, Lloyd Schwartz recently observed, "[T]he scholarship on Girl with a Pearl Earring reveals that the pearl isn't really a pearl […] the famous pearl is probably just glass painted to look like a pearl."*  It is interesting to note that the painting was executed in 1665-6, within five years after three reprints of Neri’s book, two in Italian one in English, and only a couple of years before a Latin edition printed in Vermeer's own country.

Around 1680, a Parisian maker of rosary beads invented a type of artificial pearl consisting of a small hollow glass bead, painted on the inside with the iridescent discharge of fish scales mixed with glue. He then filled the beads with wax. Jacquin had apparently rediscovered the shimmering pearly residue of a specific fish. His innovation fueled a new industry; he called the precious pigment "essence d'orient." But the material had already been employed in eastern France in 1656 and according to other reports as early as the reign of Henry IV of France (1572–1610), which closely coincides with Antonio Neri's own lifetime. By 1716, scientists were investigating essence d'orient under a microscope. Rene Antoine Ferchault de Reaumur reported tiny, perfectly formed rectangular plates that reflect the light to cause the shimmering.**

Perhaps more interesting than who discovered what, is the exchange of ideas and the overlap of interest between an Italian alchemist, a British queen, a Dutch painter, a French jeweler and a biologist.

* Also see Anthony Bailey, A View of Delft: Vermeer Then and Now (London: Chatto & Windus, 2001), p. 123, 124.
** For an English summary see The Edinburgh Philosophical Journal October 1839-April 1840 (Edinburgh: Adam & Charles Black, 1840), v. 28, p. 114, 115.

Glass Salt

Diderot & d'Alembert, L'Encyclopédie (1772)
Raking Out Baked Frit

Making glass from raw materials involves several steps. In his 1612 book on glassmaking, L'Arte Vetraria, Antonio Neri breaks the process down into parts so that, "given a bit of experience and practice, as long as you do not purposely foul-up, it will be impossible to fail." Pure white sand, or preferably quartz river stones which Neri calls "tarso" is broken up and pulverized into a fine powder. The initial work can be done by heating the stones in a furnace, then dropping them into a vat of clean cold water, where they will fracture due to the thermal shock. The process was often repeated multiple times. From there, the pieces are pulverized in a stone mortar and pestle. Stone, because metal tools would contaminate the quartz, and in the end tint the glass. Finally, a powder is obtained by grinding with a stone tool on a flat granite "porphyry stone." This powdered quartz is the main ingredient of glass.

The second critical ingredient is the flux, what Neri calls "glass salt" or "soda." This can be obtained from mineral sources, but European glassmakers in the seventeenth century extracted all their salt from certain plants. The powdered quartz was mixed with the salt and a third ingredient, which is critical, lime. Lime is simply calcium oxide used by builders to make cement. It is nothing more than pulverized seashells roasted to a high temperature. Neri advises using two pounds of lime for every hundred pounds of salt. He specifies that it should be added to all his frit recipes, but it is not clear that he understood its critical importance; without lime, the glass would be subject to attack by mere water, eventually decomposing. This mixture of soda, lime and silica when heated in a kiln would chemically react forming "frit." The combined materials were raked around in a kiln for a long period (many hours) and finally formed nut sized pieces. It was cooled and heaped into piles in dry cellars where it was aged for a time. This is where some real "magic" in glassmaking takes place. The glass salt or soda dramatically lowers the melting temperature of the quartz, all the way down to a point that was easily achieved in a wood fired furnace. When a batch of glass was made, the aged frit was then melted in furnace crucibles and skimmed to remove excess salt, which floated on the surface; it could foul the glass, and smelled terrible. The melted glass, now ready to work, was sometimes colored and finally made into objects by gaffers. 

Neri obtained his glass salt from products shipped by traders from the Levant (eastern Mediterranean). It was supplied as the dried, partially charred remains of special plants that grow in arid seaside conditions. Shipping them this way cut down on weight and volume, and prevented rotting. These Soda and Kali plants contain large amounts of sodium carbonates. This is a white powder, chemically identical to what we know as "washing soda." He advises, 

In buying either of these make sure it is richly salted. This may be determined by touching it with the tongue in order to taste its saltiness; but the surest way of all is to do a test in a crucible and to see if it contains much sand or stones, a thing common in this art and very well known by glass conciatori.

He crushes any large pieces of the product in a stone mortar, and sifts the result through a fine screen, ensuring that most of what remains is salt.  

As the common proverb of the art of glassmaking says: a fine sieve and dry wood bring honor to the furnace. Then with any of these sodas, 100 pounds of soda ordinarily requires 85 to 90 pounds of tarso.

Neri sets up large cauldrons of clean water over brickwork stoves, adds the plant product and boils the water. He strains the insoluble parts out and reduces the liquid by evaporation until crystals of the salt start to form on the surface. He skims these off and continues the process. Finally he carefully dries the product. Our glassmaker describes several variations of this process, including one in which he takes extreme measures to ensure the purity of the salt and clarity of the finished glass. In all, this is a task that could easily take several weeks to perform for the amount of frit to fill a single pot for the gaffer to work.

Not content with the established materials, our glassmaker experimented extensively with other plants: 

[U]se the husks and stalks of fava beans after the farmhands have thrashed and shelled them. With the rules and diligence prescribed for the Levantine polverino salt, extract the salt from this ash, which will be marvelous, and from which a frit can be made using well-sifted white tarso, as is described throughout this work. A very noble frit will result, which in the crucible will make a crystal of all beauty. The same may be made from the ashes of cabbages, or a thorn bush that bears small fruit, called the blackberry, even from millet, rush, marsh reeds, and from many other plants that will relinquish their salt. *

*These other plants produce potassium carbonate salts with similar properties to sodium carbonate.

The Rise and Fall

"Merry Company," (1623)
Gerard van Honthorst

The first decade of the seventeenth century was a golden era for glass in Tuscany. The Venetian techniques brought to the region by Grand Duke Cosimo de' Medici in the 1570s had been assimilated. The pioneering work of his son, Francesco, in cross pollinating different crafts under one roof, was by now bearing fruit. Grand Duke Ferdinando understood the value of glass as a source of prestige and was willing to invest in it. This was the environment in which Antonio Neri first learned to make glass. Delicate drinking glasses were the toast of the aristocracy throughout Europe. The material was critical to the advancement of chemistry, medicine and by the end of the decade astronomy. 

In 1602, Antonio Neri came to work in the shop of Niccolò Sisti in Pisa. While Sisti was making fancy glassware for the Medici court, the nearby Coscetti firm was supplying Pisa with everyday items. Coscetti made glassware for private homes, but also innkeepers, spice and perfume sellers, winemakers and a baker among others. Their wares included cruets for oil, saltcellars, carafes, drinking glasses, containers for holy water, reliquaries, gilded Venetian style cups and English style flasks. 

By the second decade, momentum started to shift and before long, the glass industry in Tuscany fell on hard times. Apparently the demand for glass could not support the number of factories that had started and the rapid succession of leadership in the duchy added uncertainty to patronage of the arts in general. 

Another factory in Pisa was run by Giovanbattista Guerrazzi, who had acquired the exclusive right to make Venetian style cristallo from Neri's old employer Sisti. In 1623, Guerrazzi had problems of a different sort, not directly related to the sales of glass. He appealed to Pisa’s Office of Rivers and Ditches, pleading with them to modify a recent ruling. He explained that he owned three houses next to his furnace, one for his family and the others functioning as sales space and housing for his workers. Since he was the exclusive maker of cristallo, he had employed a number of girls and women to decorate the delicate glassware, and a constant stream of the nobility showed up to watch the work being done. Guerrazzi's problem was that the Magistrate of Public Decency had recently published a list of seven places where women of "ill repute" were allowed to stay. One of these was located next door to his glassmaking operation. He begged for a change in the ruling, to move his new neighbors elsewhere.

The outcome of his appeal is not known, but Guerrazzi was succeeding in the glass business, and at the same time accelerating the demise of his competitors. He bought-out and demolished the furnaces of a number of other glassblowers and planned the same fate for the Coscetti operation, putting all the craftsmen there out of work. In the mid 1620s, after a quarter century of operation, the fires under Coscetti furnace were allowed to go out forever. Furnaces at Leghorn, Pistoia and Prato had shuttered, leaving only the one furnace in Pisa, two in Florence and two at the castle of Montaione. 

Royal Apothecary

Fresco, early 16th century speziale,
Castello di  Issogne, lower Aosta Valley, Italy.

As physician to the Medici royal family, Antonio Neri’s father (Neri Neri) worked closely with the other medical professionals in Florence. Among them was Stefano Rosselli, the royal pharmacist, who owned the Speziale al Giglio in the center of town.  We would readily recognize this shop today; rows of labeled jars lined the walls holding exotic remedies and ingredients from around the world. Freshly made sweets, cakes and other confections sat on the counter to entice customers. 

One of several such shops located around the city, ‘speziali’ dealt with medicines and herbal remedies, but also a wide variety of other needs, from pigments for artists, to the distillation of spirits, to the rental of funerary equipment, to raw materials for alchemists. Each shop had its own specialty to distinguish itself from the others. To some extent, they also competed with private operations run by convents and monasteries. Rosselli’s shop was famous for catering to the Medici family and courtiers, and as such he could command premium prices. But the function of these shops was not all business; they also proved popular meeting places for the local intelligentsia. Poetry, literary and other groups with various interests often congregated in the back rooms of the speziali.

Stefano Rosselli came from a family that was a mixture of artists and pharmacists. His father Romollo, with a degree from the university at Pisa, was a specialist in herbal remedies (simples). His brother Antonio (Fra Anslemo) worked at the pharmacy of San Marco, directly across the street from the Casino where Antonio Neri would later make glass. Their grandfather Bernardo Rosselli was a painter, a favorite of Michelangelo. Stefano’s daughter Fiametta joined the Dominicans as a nun, and became the famous sculptress Suor Caterina Eletta. A distant cousin was Cosimo Rosselli, who returned from Rome with a small fortune, earned painting for the pope. Biographer Giorgio Vasari noted that Cosimo could have lived comfortably on those earnings had the passion for alchemy not overtaken him. 

Stefano proudly maintained a proprietary list of treasured recipes gathered over a lifetime of experience. Some were given to him directly by Grand Duke Cosimo de’ Medici, his son Francesco and daughter Isabella. Between 1589 and 1593 when Rosselli was in his late sixties, he started to compile these into three notebooks, which he eventually passed down to his sons and today have survived the ravages of time. The three books are devoted to medicines, perfumes and confections. Antonio Neri was a teenager in this period, and it is easy to imagine an occasional visit to the Speziale al Giglio for a piece of something sweet, perhaps one of Rosselli’s excellent pistachio calissons.

For a transcription and French translation of the recipes see: Rodrigo de Zayas, Mes Secrets, à Florence au temps des Médicis 1593 (Paris: Jean-Michel Place, 1996).

Metal Veins of the Earth

Antonio Neri, "The Mineral Gold"
Ferguson 67, f. 5r.

Over a decade before Antonio Neri wrote L’Arte Vetraria, the book on glassmaking for which he would become famous, he wrote an illustrated manuscript on the subject of alchemy. Begun around 1598 and completed in 1600, this is Neri's earliest known work, written very shortly after he was ordained as a Catholic priest. 

The illustrations are divided between technical depictions of chemical apparatus and allegorical images meant to show philosophical relationships within the natural world. Two of Neri's pictures from this latter group, respectively, show veins of gold and silver growing in the earth. The veins are depicted exactly like the arteries of an animal. In both pictures, they radiate out around a fiery hole in the ground. Overhead the sun shines down on the gold and the moon over the silver. Further up in the sky, Neri shows the constellations associated with each metal; Leo the lion for gold and Cancer the crab for silver (his rendition looking more like a lobster).

Antonio Neri, "The Mineral Silver"
Ferguson 67, f. 6r.

It was no flight of fancy that mined metal and ore deposits were depicted as literal veins. It was widely thought these were living structures, which carried the earth’s nutrients. In one of Neri's final works, his 1613 manuscript Discorso, he explains the ancient theory that gold could occur as immature seed material, left over from the primordial creation. If properly nourished, this seed would mature and grow into the precious metal, and with the appropriate knowledge this natural process could be restarted, or accelerated and the gold could be brought to perfection by artificial means. 

The idea that mined mineral deposits could regenerate naturally, if left to rest, is an ancient concept, one that persisted long past Neri’s era. In 1814, writing about tin mining in "On the Veins of Cornwall," William Phillips complained to the Geological Society of London, that armed with some current scientific knowledge, "nor would many miners […] believe, even to this day, in the regeneration of metals." Phillips quoted from an 1811 survey by Tonkin, in Carew's survey of Cornwall: "Whether tin doth grow again, and fill up places which have been formerly wrought away, or whether it only seperateth itself from the consumed offal, hath been much controverted, and is not to this day decided." And  "whether—dead lodes—that have not one grain of tin in them—may not hereafter be impregnated,  matured,  and prove a future supply to the country, when the present lodes are exhausted, I think well deserves our highest consideration."  

At base, this is not superstition nor wild speculation, but rather considered judgments of thoughtful men making careful observations. Mines were often attended by acidic or other caustic liquids, either produced naturally or by washing operations, which leached out and dissolved various solubles. These liquids could sometimes dissolve metal out of ore and redeposit it elsewhere. Abandoned mines, it was noticed, could exhibit new crystal growth after a period of years or centuries. Today, the redeposition of minerals is a well accepted phenomenon, however, where it does occur it takes place not on a human time scale, but on a geological one, over millions of years.