The internet serves as a valuable resource, but it also struggles to maintain the accuracy of the information available to the public. A prime example of this issue is the term "micromosaic" or "micro mosaic" which has become a widely adopted term applied to "mosaics." Only occasionally do we encounter listings that refer to these items by their correct name. This trend of misnaming has persisted for approximately a decade, leading many individuals to recognize them by the incorrect terminology. Many blogs by jewelry dealers and hobby resellers post articles using the wrong name just compounding the issue and causing even more confusion. However, this widespread usage does not alter their true classification as defined by the majority. Simply relying on Google, internet blogs and posts by non authoritative sources often leads to a proliferation of inaccurate information. Many experienced and professional sellers, who are aware of the distinction, acknowledge that "micromosaic" garners more interest, ranks higher in search engine results, and is intentionally misapplied. They justify this choice by arguing that without the term "micromosaic," their products would be overlooked, given that it is the name most commonly used. Nevertheless, it remains true that two wrongs do not make a right. Thus, the challenge persists: how can we effectively differentiate between the two so that we know regardless of what a seller calls them?

First what is a Mosaic?

Mosaic is the art of decorating a surface with designs made up of closely set, small pieces of material which can be glass or ceramic or other material. The tiles that make these works of art are called tesserae which can vary considerably in size. In jewelry they can range from tesserae as large as 10 millimeters to glass threads less than 1mm called filati (spun enamel) which makes the finest mosaics look like miniature paintings. The broad category of mosaics are then broken into subgenres based on a number of factors relating to the size and assembly of the tesserae. For mosaics used in jewelry the three genres we see are noted with the historical name and (current name): Florence (pietra dura), Roman (micromosaic) and Venetian (mosaic).

Defining Micromosaic

In Italy this type of mosaic was called "mosaici minuti" which translates in English to 'minute mosaic'. Mosaicists of the Vatican Studio in Rome note for their history of micromosaic's in the paragraph titled 'Technical Aspects of a Micromosaic' in the below link that historically the dimensions of the loaf shaped tesserae or oblong rods which could be circular or cubic that are less than 1mm in diameter cross-section and not exceeding 2mm or 3mm in length. In the earlier 1800's when the technique progressed to finer threads, the filati were cut into even finer more minute tesserae. https://www.micromosaico.it/hi... The "mosaici minuti" were originally refered to historically as 'Roman mosaic's' but this classification was thought to be a misleading term for them as the ancient Roman mosaic's were not as fine. Also the process for making "mosaici minuti" did not exist until the later 1700's. However it wasn't until the 1970's when a noted British collector, Sir Arthur Gilbert made a distinction of the subgenre for the finer minute mosaic's by calling them micromosaic. This was a very close English translation of their given name by the Rome mosaicist's and a more accurate way to make the distinction from other mosaics that are not as fine.

• Tesserea tiles less than 1mm in diameter and 2mm to no longer than 3mm in length.   
• Tiles set in mastic vertically and stacked tightly end to end with no spaces between tiles.
• Depending on how detailed, there are hundreds up to as much as 3,000 to 5,000 tesserae per square inch.
• The tiles are sealed to fill all crevasses with wax for a completely smooth polished surface, no gaps and no spaces between the tiles.(unless wax has dried out or is damaged).
• The completed work is so fine it resembles a painting.

Defining Mosaic

These are both mosaics the very course tiles of a 20th century mosaic on the left and the older 1880's Venetian mosaic on the right that has closely stacked tiles that are waxed on the surface but larger than the tiles used in micromosaics. There are some very fine mosaic's that bridge both, some even are a combination of the two. When both techniques of using fine and larger tesserae are combined in a mosaic, the finer examples of mosaic's do tend to be designated as micromosaic in this case. Are they technically a micro? no...most are not but when they are close enough even the experts will classify as a micromosaic because that is the desirable technique for buying and selling. Historically this type of mosaic was classified as a Venetian mosaic to differentiate them from the finer Rome mosaics. Today the Venetian mosaics are refered to as just mosaic, although some experts still use the traditional term too.

• Larger tesserae that is wider than 1mm in diameter or cross section and longer than 3mm. 
• Millefiori glass tiles used as quick way to add designs, flowers and shapes vs using separate colored tiles to build the design.
• The design is course with larger tiles in various shapes.
• Tiles can be set horizontal / lengthwise, vertical or combination of both that may or may not stacked tightly together. 
• Tiles are not sealed or polished smooth, however finer mosaic's like the one on the right above, may be waxed but that alone does not make them a micromosaic. 

Below are several old catalog pages for mosaic jewelry that date from 1911 to 1927. You can see the designs that were called mosaic and how today many are misidentifying them. These examples are what would be considered finer mosaics but they are still easy to discern. 

Mini Mosaic

Mini mosaic or miniature mosaic is a term that is not used or recognized by jewelry historians or appraiser's of mosaic jewelry. In jewelry mosaics are either classified as micromosaic or mosaic for distinction purposes. Artisan's tend to call their works micro, mini or miniature mosaic's regardless of the technique used to make theirs or the size of their tesserae. This is because many feel that in comparison to larger mosaic wall murals and floor mosiacs that their work is micro or mini. However when mosaic's are in jewelry the long established distinctions between only the two very different types, micromosaic or mosaic, are applied. In this case a mini or miniature mosaic would be classified as a mosaic. 

Occasionally, an appraiser encounters an item that defies conventional comparison in the marketplace, making it challenging to assign a value. When faced with the task of evaluating an item that is not only difficult but impossible to replace due to the depletion of resources, it becomes a complex undertaking. In such cases, appraisers review the historical records of auction houses to find similar items, but there are instances where no comparable items can be found. What happens then?

Such a scenario arose a couple of years ago, making it a truly unforgettable experience. In this specific case, the items being appraised were part of a collection of jewelry from Red Skelton's widow, adding significant historical and cultural value to the pieces. These unique pieces, all custom-made by William Ruser, a renowned Beverly Hills Designer in the mid-1900s, were auctioned through Auctioneer Jones & Horan in Goffstown, New Hampshire. I can post the items without breaking confidentiality as the owner wanted them publicized by the auction house in their advertising who these items were worn by, as it would significantly impact auction results and generate more interest having this provenance known. 

The challenge of valuing items with no replacement or comparison was particularly evident in the appraisal of the two massive in size star sapphires, weighing approximately 62 and 68 carats, an exceptionally rare find even for 75 years ago. Given the absence of similar star sapphires of such size, we (myself and Jonathan of Jonathan’s Jeweler’s the store where the appraisal was conducted at) needed to consult the expertise of a renowned gemologist, a regular contributor to the Gem Guide, who is a prominent resource for current market pricing of gems. The gemologist's opinion suggested a significant value in the higher five-digit range but also noted that we could even go as high as a six-digit range on each gem, reflecting their irreplaceable nature in today's market. Ultimately, the assigned retail replacement value was aimed to cover the irreplaceable nature of the gems in the event of a loss, acknowledging the challenge of not being able to find suitable replacements in the current gem market today.

It's Glowing Fluorescent Green...That Means Uranium Glass! Or does it?

It is a common sight to see individuals in the glass and gem community using UV (black) lights to illuminate their stones, often proclaiming, "This is uranium glass!" if a bright green glow is observed. In many instances, the glow is not bright or even green, yet the mere presence of fluorescence leads some to conclude that uranium must be the cause. However, is this single tool sufficient for accurate identification, or does it require a more comprehensive approach? The answer lies in possessing advanced gemological knowledge and equipment, recognizing that UV test results are merely indicators that should be used along with further testing to reach a conclusion.

Ultraviolet fluorescence is an unreliable standalone property for gem identification due to its variability. Minerals of the same species can exhibit different fluorescence colors depending on their origin. The intensity of fluorescence can also vary, ranging from inert to strong within the same species. Moreover, different minerals can fluoresce the same color, rendering accurate identification based on color alone unreliable. 

Uranium glass rhinestones. Could be vintage and new. Mostly seen in costume jewelry or crafter/artisan set in new jewelry.	Synthetic spinel, mint green or green. This is what is used in fine jewelry and commercially produced mid century jewelry in gold and silver. Some costume jewelry makers used synthetic gems too.	Modern jewelry from mid 1970s to present for cubic zirconia that is doped with erbium as a colorant for pink and purple. Erbium as well as selenium is also used in glass for a green glow.

While uranium glass is undoubtedly famous for its green fluorescence, other elements and compounds can trigger a similar effect under UV light, leading to misidentification. Here are some common culprits:

• Manganese: Manganese, particularly when used as a decolorizer, can cause glass to glow a yellow-greenish hue under UV light. This is especially common in antique clear glass, which may appear slightly lavender or amethyst in daylight due to manganese exposure to sunlight.
• Selenium: Selenium can also cause a green glow, albeit typically a weaker and more yellowish-green than uranium glass. It's commonly used in red and orange glass and can sometimes be found in clear glass.
• Modern Glass with UV-Reactive Agents: Some modern glass manufacturers intentionally add UV-reactive compounds to their products to achieve a similar green glow. These agents mimic the effect of uranium without containing any radioactive material.
• Plastic and Other Materials: Certain plastics and other materials can also fluoresce under UV light, adding further confusion to the identification process.

Yet another variable to add to the list, is what wavelength your UV light is. Is it 365nm or 395nm? The fluorescence results will differ and you need to know to which it is. As such, UV testing, in conjunction with other gemological tests, can be a useful tool, but should not be the sole method of identification. You can see below that manganese glass is also commonly misidentified as uranium glass when the wrong UV light is used.

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