Material Characteristics

Zellige

Material Characteristics and Possible Imperfections

Handmade zellige tiles and mosaics contain visible variations arising from natural clay, individual glazing, firing, and hand finishing. Their color, texture, dimensions, and edges can differ within a single order, and additional changes may become apparent during handling, grouting, environmental exposure, or use. The characteristics described here include ordinary cosmetic variation and possible damage or deterioration. Their extent and effect on the material's integrity vary; inclusion in this document does not establish that every condition is acceptable or present in every order.

What to expect

Color range and visual differencesTiles within one named color may differ in shade, warmth, undertone, saturation, and gloss. A single piece can contain light and dark areas, mottling, clouding, streaks, or changes in translucency. Daylight, artificial lighting, shadows, and viewing angle can alter how these differences appear. Samples represent only part of the available range; delivered material, later replacements, separate batches, and different formats may not match exactly.
Glaze coverage and poolingGlaze thickness and coverage may be uneven. Where glaze collects at an edge or in a depression, it can appear darker, deeper, or more reflective. Thinner areas may look lighter or allow more clay color to show through. Small patches may be partly glazed or bare. Crawling describes glaze drawing back during firing and leaving a defined or irregular uncovered area
Pinholes and other surface openingsSurface openings can include pinholes, pits, cavities, dimples, and crater marks. Pinholes may remain where gases escape during firing, either individually or in groups. Larger depressions may retain glaze or expose the clay. A crater can have a recessed center with a rough or raised rim. Glaze bubbles and blisters may remain closed, become fragile or sharp, or break open to leave a cavity.
Raised texture and mineral markingsBumps, rounded protrusions, ripples, and gently undulating areas may interrupt the face and produce uneven reflections. Natural ingredients and firing can also leave iron spots, dark flecks, or isolated color marks. Mineral inclusions may create localized surface interruptions; lime pops are described in some Zellige literature as small displaced areas that expose the body. Active or recurring loss can involve deterioration beyond a stable cosmetic mark.
Exposed clay and delivery residueBare clay can be visible along corners, edges, cuts, pits, or chipped areas. The back is generally unglazed, and field-tile edges may also be unfinished. Exposed clay is more absorbent than the glazed face. Clay powder, packing dust, and other delivery residue may be present separately from permanent markings within the fired coating.
Crazing and body cracksFine intersecting lines within the glaze are known as crazing. They relate to differences in the expansion and contraction of the coating and its clay support, and may become more apparent with time, moisture, dirt, or grout pigment. A line extending into the clay is a body fracture. Deeper cracks may pass through the tile, widen, separate corners, or divide a piece into movable fragments, affecting integrity as well as appearance.
Size and shape variationLength, width, thickness, squareness, and edge angle can vary between pieces and across one tile. Nominal measurements identify the general format. Outlines may be curved, tapered, uneven, or out of square, while faces may be bowed, cupped, or twisted. Edge slopes, small notches, roughness, and cutting marks may remain visible. A newly cut perimeter can reveal a different profile or additional bare clay.
Chipped edges and uneven jointsNicks, scalloped edges, missing corner tips, and localized chips may result from hand finishing or handling. Loss can involve glaze alone or part of the clay and may extend onto the face. Its visibility depends partly on the contrast between glaze and body. Uneven outlines can create joints that vary in width or direction; differences in thickness and flatness can leave neighboring faces at different heights, known as lippage, with stronger shadows or projections.
Mosaic alignment and sheet variationMosaic units retain the color differences, pits, crazing, chips, texture, and thickness variation of their source tiles. Hand assembly can introduce unequal spacing, slight rotation, shifted positions, and changes in alignment or motif proportions. Differences between sheets may reveal a grid, band, or interruption in the pattern. Borders, corners, and intersections can have irregular gaps, while cut edges may show small chips or exposed clay.
Loose mosaic piecesIndividual mosaic pieces may loosen or separate from their mounting during transport, handling, or positioning, and movement or detachment may become noticeable during grouting. The condition of the mounting and the bond within a completed surface are separate aspects of the assembly.
Chipping and glaze separationSmall fragments of glaze or clay may come away during unpacking, cutting, drilling, setting, spacer removal, grouting, or cleaning. Thin corners, raised glaze, existing chips, and surface openings can be vulnerable to contact or pressure. The coating may also separate as flakes, slivers, or larger patches. Shivering is one ceramic condition associated with glaze fit that can cause separation. Repeated shedding, sharp flakes, and extensive peeling differ from an isolated stable chip; the timing of their appearance does not establish the cause.
Scratches and surface residueTools, grit, rough pads, contaminated sponges, and construction debris can leave scratches, scuffs, or reduced gloss. Abrasion may stand out on dark or reflective finishes. Tape and protective films can leave adhesive deposits, pull marks, or changes in sheen, and their removal can dislodge vulnerable glaze. Dried grout, mortar smears, and other construction deposits may form cloudy films or rough patches that obscure the original finish.
Grout retention and pigment stainingGrout may remain within pinholes, pits, chips, and crazing, making the openings lighter, darker, or more defined. Pigment can lodge in fine lines or absorb into exposed clay, leaving contrasting dots, outlined cracks, darkened edges, or localized stains. These changes can become a lasting part of the visible surface.
Chemical and sealer effectsIncompatible chemicals or aggressive cleaning treatments can dull, discolor, or damage the coating. Surface treatments and sealers may deepen the apparent color, change reflection, or leave streaks, uneven sheen, haze, or a residual film. These effects depend on the particular finish, product interaction, and exposure.
Moisture and white depositsAbsorbent clay can darken when damp, especially on unglazed pieces or exposed areas within a glazed face. Some moisture changes are temporary, while persistent discoloration can have another cause. Oils, grease, colored liquids, and other contaminants can leave absorbed stains that remain after drying. Pale residue may consist of grout, cleaner buildup, minerals, or efflorescence. Efflorescence forms when moisture carries dissolved salts to the surface and leaves a deposit as it evaporates.

Review and approve your actual lot before installation a sample shows character, not an exact match. Blend tiles or mosaics from several boxes as you install, and order 20-30% extra to allow for cutting and selection.

Terrazzo

Material Characteristics and Possible Imperfections

Cement-based terrazzo combines stone aggregate, and sometimes glass, with a pigmented cement binder. Casting, curing, grinding, and finishing reveal a surface whose individual fragments and background are not perfectly repeated. The descriptions here concern genuine cement-based terrazzo tiles; resin-based systems and porcelain with a printed terrazzo design have different characteristics. The following characteristics may be visible on delivery or develop during handling, grouting, exposure, or use. Their presence and severity vary by composition and finish. Some are ordinary cosmetic variations; others involve damage or deterioration. Inclusion in this document does not establish that every condition is normal, acceptable, or present in every order.

What to expect

Color variation and sample differencesThe cement background and stone chips can differ in shade, undertone, and saturation between pieces or production batches. Mottling, cloudy areas, or uneven color concentration may be visible, particularly in strongly pigmented backgrounds. A sample shows only a limited portion of this range, and later orders may differ from the original material.
Aggregate size and distributionStone fragments vary in shape, orientation, size, and position. Some areas contain a dense concentration of chips; others show more of the cement background. Larger fragments may appear only partly within an individual tile or intersect a cut edge. Adjacent pieces do not form an identical or continuously matching stone pattern.
Natural markings within the stoneIndividual aggregate pieces may contain veining, mineral markings, fine lines, or changes in color. These features can remain visible after grinding. A natural line confined to a stone fragment has a different significance from a fracture continuing through the surrounding binder or across the tile.
Pinholes and open poresSmall air pockets left during casting can appear as pinholes or open pores in the finished face. Larger recesses may resemble pits, shallow dimples, or cavities. Their number and visibility vary, and grinding may expose openings that were previously below the surface. Filled pores may also be visible where filling forms part of the finishing process.
Uneven texture and polishing marksThe cement and embedded stone can respond differently to grinding, producing subtle differences in texture or reflection. Fine abrasive marks, light swirls, small depressions, and variations in sheen may be visible under certain lighting. Honed, polished, and textured finishes naturally have different appearances; pronounced polishing defects are distinct from slight finish variation.
Dimensions and flatnessLength, width, thickness, and squareness may vary within the product tolerances. Slight curvature or differences in surface flatness may also occur. Nominal dimensions identify the general format rather than guaranteeing identical measurements for every piece. Geometry and placement can contribute to unequal joints or height differences between neighboring faces, known as lippage.
Edge chips and exposed aggregateSmall nicks, rough sections, missing corner tips, or localized chips can appear at the perimeter. Cutting and grinding may intersect a stone fragment or pull a grain from an edge, leaving a small void. The exposed profile can therefore differ from the finished face, with visible cement, stone, or an irregular chip outline.
Aggregate pullout and small fragmentsIndividual grains or small pieces of cement and stone may become dislodged during grinding, cutting, handling, setting, grouting, or cleaning. The resulting opening may expose a rough recess beneath the finished face. A localized grain loss differs from repeated aggregate release or a surface that continues to break down.
Fine surface lines and deeper cracksFine lines or a small network of surface cracks may be visible in the cement matrix. Other fractures can cross both binder and aggregate, extend through an edge, or pass through the tile thickness. Widening cracks, separated portions, and movement between fragments affect material integrity. A visible line alone does not establish its depth, cause, or acceptability.
Surface deterioration and separationA damaged surface may shed flakes, lose larger patches, or become friable rather than remaining firm. Spalling describes loss from the surface; delamination describes separation within an assembly or between layers where layers are present. Extensive loss, recurring fragmentation, and separation are damage conditions, not ordinary differences in aggregate pattern.
Scratches and impact marksAbrasive grit, tools, construction debris, and contact with hard objects can leave scratches, scuffs, gouges, or fresh chips. Smooth and reflective finishes may make these marks particularly noticeable. Repeated contact can gradually reduce the original sheen or produce localized differences between exposed and less-used areas.
Grout retention and pigment stainingGrout can remain in pores, pits, and chipped areas, changing their contrast and making small openings more apparent. Pigments may penetrate the absorbent cement or lodge around aggregate, leaving dots, darkened borders, or patches of discoloration. Some grout-related stains can remain permanently; their appearance does not imply a change in the stone-chip composition.
Surface films and treatment marksDried grout, mortar smears, adhesive residue, protective wax, or other deposits can obscure the finish or create rough patches. Sealers and coatings may alter color depth and gloss or leave streaks, shiny spots, haze, and uneven reflection. The resulting appearance reflects the surface treatment or residue as well as the underlying tile.
Moisture darkening and absorbed stainsThe cement matrix is porous and can become darker or patchy when damp. Unequal absorption may make some areas change more than others. Certain moisture-related differences are temporary, while persistent marks can have another cause. Oils, grease, and colored liquids may penetrate the surface and leave absorbed stains after the tile has dried.
Acid etching and chemical discolorationAcids can react with the cement binder and marble or other acid-sensitive aggregate. The result may be dull spots, pale rings, roughness, loss of polish, or a localized change in texture. Etching is a physical alteration of the surface and differs from an absorbed stain. Other incompatible chemicals or treatments can also discolor or damage terrazzo.
White deposits and efflorescenceA pale film or powder can consist of grout residue, cleaner deposits, minerals, or efflorescence. Efflorescence develops when moisture carries dissolved salts to the surface and leaves them behind as it evaporates. Several different conditions can look similar, so the presence of white residue does not by itself identify its source.
Patina and changes in surface stabilityUse can gradually change the sheen, color impression, and surface texture, creating a patina. Separate from ordinary wear, cracks can develop or extend across an installed surface, and tiles or portions of an assembly may lose attachment. Movement in supporting materials and other assembly conditions can contribute to such changes; timing alone does not establish responsibility or cause.

All Stones

Material Characteristics and Possible Imperfections for marble, limestone, and travertine

Marble, limestone, and travertine are natural materials whose appearance reflects their geological formation, mineral composition, quarry source, and method of finishing. These descriptions apply generally to stone tiles and cut pieces, including mosaics. Individual varieties differ in porosity, strength, texture, and response to exposure; a characteristic common in one stone may be uncommon in another. The following descriptions include inherent visual features, manufacturing and finishing variations, and conditions that can develop during handling, grouting, or use. Some are ordinary cosmetic characteristics; others can affect integrity or indicate deterioration. Their inclusion does not establish that every condition is acceptable or that every stone will exhibit it.

What to expect

Color range and sample differencesColor, undertone, shading, and the concentration of markings can change between pieces, blocks, quarry areas, or production lots. A single tile may include contrasting patches or cloudy areas. Samples and photographs show only part of this range, and replacement pieces may differ from the original order. Lighting and viewing angle can further change the apparent color and reflection.
Veining banding and pattern directionVeins, streaks, bands, and mineral seams can vary in width, color, direction, and density. Some pieces may be strongly marked while others from the same material appear relatively quiet. Cutting across or along the stone structure can produce noticeably different patterns. Veining is particularly prominent in many marbles, while vein-cut and cross-cut travertines can have distinctly different appearances.
Fossils shells and mineral inclusionsShell fragments, fossils, crystalline areas, speckles, and other mineral inclusions may be visible within the stone. Fossils are characteristic of many limestones, and their size and distribution are naturally irregular. These markings may contrast strongly with the surrounding background and do not repeat predictably from piece to piece.
Pores pits and natural cavitiesSmall pores, pinholes, shallow depressions, and larger cavities may interrupt the face or edges. Their interiors can be smooth, granular, or irregular. Travertine commonly contains a network of natural voids, while some limestones and marbles also display small openings. The number and visibility of cavities depend on the stone, cut, finish, and whether the product is supplied filled or unfilled.
Surface finish and reflectionHoned, polished, brushed, tumbled, and other textured finishes reveal the same stone differently. Minerals and filled areas can respond differently to finishing, creating subtle changes in sheen, texture, or reflection. Fine abrasive marks or localized unevenness may also be visible. Pronounced tool damage or an unsuitable finish is separate from ordinary mineral-related variation.
Dimensions and surface alignmentLength, width, thickness, squareness, and flatness can vary within the product specification. Edge profiles may be straight, beveled, clipped, rounded, or intentionally distressed, depending on the selected finish. Geometry and placement can produce unequal joint widths or differences in height between adjacent faces, known as lippage. Nominal dimensions do not establish identical measurements for every piece.
Fissures seams and deeper cracksNatural fissures and mineral seams may appear as fine lines or separations within the stone. A vein is a mineral pattern and is not automatically an open fracture. Other cracks can cross the stone, widen, split an edge, or extend through the thickness. A visible line alone cannot reliably establish its origin, stability, or acceptability; movement or separated portions involve more than appearance.
Filled areas and factory repairsSome stone is supplied with pores, holes, fissures, or localized repairs filled with cementitious material, resin, or epoxy. These areas can differ from the surrounding stone in color, translucency, texture, or polish. Fill may be more apparent under angled light or along an exposed edge. Its presence alone does not establish either a defect or the adequacy of the repair.
Reopened holes and loss of fillA filled surface does not mean that every cavity within the body has been reached. In travertine, a thin layer of stone can conceal a void until pressure or wear breaks through it, exposing a new opening. Existing fill can also become loose or fall out. A newly visible hole may therefore reflect a concealed cavity or loss of filling rather than a change in the overall stone composition.
Chipping and surface breakdownSmall nicks, missing corner tips, or chips may occur along edges, on cut faces, or within a visible surface. Vulnerable grains, thin areas, and material around cavities may release fragments during cutting, handling, setting, grouting, or cleaning. Spalling, flaking, recurring powdering, and larger losses describe deterioration or damage conditions rather than ordinary differences in stone pattern.
Scratches and developing patinaGrit, abrasive contact, tools, or hard objects can leave fine scratches, scuffs, nicks, and localized loss of polish. Their visibility depends on the stone and finish, with smooth reflective faces often showing marks more clearly. Repeated use can gradually change the sheen and edge appearance, producing a patina that differs between heavily used and less exposed areas.
Moisture darkening and absorbed stainsNatural stone absorbs moisture to different degrees and may become darker, patchy, or uneven in tone when damp. Some changes diminish as the material dries; persistent discoloration may have another cause. Oils, grease, food, cosmetics, and colored liquids can penetrate absorbent areas and leave lasting marks. Filled areas may respond differently from the surrounding stone.
Acid etching and chemical effectsMarble, limestone, and travertine are generally sensitive to acids because of their carbonate composition. Exposure may leave dull spots, pale rings, roughness, or a change in surface texture. Etching alters the stone itself and differs from an absorbed stain, although both may occur together. Other incompatible chemicals can also affect the finish or existing fillers and coatings.
Rust and metallic stainingOrange, brown, green, or other metallic discoloration can occur where the surface is affected by metal-related staining. Rust-colored marks may be associated with iron-bearing materials or contact with metal objects. The color and shape of a stain do not, by themselves, establish whether it originated at the surface, within the stone, or elsewhere in the assembly.
Grout residue and surface treatment marksGrout or other residue may remain within pores, pits, joints, and textured areas, changing their contrast. Adhesives, sealants, waxes, or coatings can leave films, smears, oily marks, or differences in reflection. Pigment or liquid absorption may also create staining near an edge or cavity. These appearances are distinct from the original veining, fossils, and mineral pattern.
White deposits and mineral filmsWhite powder, pale crusts, water rings, and cloudy films may arise from different causes, including mineral deposits, cleaning residue, or efflorescence. Efflorescence forms when moisture carries dissolved salts toward the surface and leaves them behind as it evaporates. Similar-looking deposits can have different origins and are not automatically evidence of a defect in the stone itself.
Weathering and loss of attachmentEnvironmental exposure or adverse assembly conditions can contribute to cracks, surface loss, or changes in stability. In some cases, lines continue through neighboring pieces or joints, and a tile or portion of stone can loosen or detach. These conditions differ from stable natural markings. Their cause depends on the stone and circumstances and cannot be determined solely from when they become visible.

Porcelain

Material Characteristics

Porcelain mosaics consist of small fired tiles arranged on sheets. A mesh attached to the back holds the individual pieces in a pattern and remains part of the finished assembly. This description covers glazed and unglazed porcelain mosaics with rear mesh backing. Appearance and performance depend on the particular tile, surface finish, mounting material, and intended use. The following descriptions explain visual variations and conditions that may occur during manufacture, transport, handling, grouting, or use. Slight alignment and spacing differences can occur within a mesh-mounted sheet and between adjoining sheets. Other conditions, including significant cracking, glaze separation, or loss of attachment, involve damage or performance concerns. Their inclusion here does not make every occurrence acceptable.

What to expect

Color variation and pattern differencesColor, undertone, shading, printed markings, and surface contrast may differ between pieces and production batches. Some collections are deliberately varied; others have a more uniform appearance. Stone-effect or decorative patterns can repeat or change direction across a sheet. A small sample or photograph may show only part of the available range, and later orders may differ from earlier material.
Texture sheen and edge appearanceMatte, glossy, polished, and textured surfaces reflect light differently. Relief, shallow depressions, mottling, and uneven-looking color may form part of the specified design. Molded or beveled edges can create a different visual joint width from the gap between the tile bodies. A deliberate surface effect is distinct from accidental surface damage.
Pinholes pits and glaze irregularitiesGlazed pieces may exhibit tiny openings, shallow craters, or blisters associated with the glazing and firing process. Localized bare patches can occur where glaze has drawn away, a condition known as crawling. Small raised spots or bumps may also interrupt the surface. These are possible manufacturing imperfections and are not universal characteristics of porcelain mosaics.
Glaze crazing and deeper cracksCrazing appears as a network of fine cracks in the glazed coating. It differs from a fracture that extends into or through the porcelain body. Crackle effects may be intentional in a specifically described finish; unexpected crazing or deeper cracks require a separate assessment. Fine lines alone do not establish the depth or cause of a fracture.
Small alignment and spacing differencesIndividual pieces may sit at slightly different angles or positions on the mesh. Minor rotation, offsets between rows, and small variations in the gaps between pieces can occur within one sheet or from sheet to sheet. These differences may become more noticeable in straight rows, geometric patterns, or contrasting grout. Mesh mounting does not guarantee mathematically identical alignment at every joint.
Sheet dimensions and visible joinsOverall sheet dimensions and the spacing at sheet edges may vary slightly. Joins can appear as wider or narrower lines, interrupted rows, or a visible outline around individual sheets. The appearance can reflect mounting variation as well as how adjoining sheets meet. A pronounced grid or disrupted pattern is not automatically an intended feature of the mosaic.
Piece dimensions and surface heightSmall differences in piece width, thickness, edge shape, or flatness can affect the finished surface. Adjacent faces may sit at different heights, a condition known as lippage. Directional light and reflective finishes can accentuate these differences. Nominal sizes describe the product format; the applicable product specification determines dimensional tolerances.
Mesh movement and loose piecesThe backing is flexible, so a sheet can bend or distort during handling. A piece may rotate, shift, or become detached from the mesh during transport, cutting, or positioning, leaving an irregular gap or a missing position. Separation from the mesh does not necessarily mean that the porcelain piece itself has cracked. Repeated detachment or extensive distortion is a separate condition from a minor spacing difference.
Backing adhesive and attachment concernsMesh fibers and mounting adhesive are present on the tile backs. Excessive backing coverage can restrict direct contact between the porcelain and the setting material. Depending on the mounting system, exposure to moisture or incompatible conditions can weaken or alter the backing adhesive. The water resistance of porcelain alone does not establish the suitability of the complete mesh-mounted sheet for prolonged wet exposure or immersion.
Chipping and glaze lossSmall edge nicks, broken corner tips, or face chips may occur during handling, cutting, setting, or grouting. A chip can expose a body color that differs from the glazed face. Glaze fragments may also loosen or come away, exposing the porcelain beneath. Flaking, peeling, or recurring glaze loss is a damage condition and should not be described as routine cosmetic variation.
Scratches scuffs and surface wearAbrasive particles, hard contact, or tools can leave fine scratches, scuff marks, or localized dulling during work or subsequent use. Polished and reflective finishes may show fine marks more readily. Repeated abrasion can alter the sheen or retain dirt in scratched areas. Porcelain is durable, but its surface is not immune to damage.
Grout haze and trapped residueGrout, adhesive, or other residue can remain on tile faces, along edges, or in textured recesses. This may appear as a pale film, cloudy patches, streaks, or reduced gloss. Pigmented grout can leave contrasting particles or discoloration in surface texture or micropores, particularly on certain polished finishes. These deposits can change the apparent tile color without representing a change in the original decoration.
Stains films and chemical effectsInks, dyes, oils, and other contaminants may leave marks on some porcelain finishes despite the material’s low absorption. Wax, sealer, detergent, or other films can create uneven reflection or apparent dullness. Incompatible chemical exposure can affect certain glazed or polished surfaces. A visible mark may be residue, staining, or surface alteration; appearance alone does not establish which has occurred.
Cracks and loss of attachmentA mosaic piece may develop a hairline fracture, split, or loosen within the finished surface. Cracks may also continue across several pieces or joints. Separation of a piece from the completed assembly is different from a loose piece on an uninstalled mesh sheet. The cause can involve the tile, mounting system, bond, support, or service conditions and cannot be determined solely from when the condition becomes visible.