He obviously doesn't want to be there getting yelled at by some guy with a carb crazing and a $400 scooter.
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The oblong eggs, up to about 3 inches (7.2 cm) long, were pliable with a thin, hard outer layer marked by cracking and crazing covering a thick membrane inner layer, resembling soft eggs of some modern snakes and lizards.
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A Song dynasty Celadon vase with crazing glaze A close view of ceramic glaze crazing Crazing is the phenomenon that produces a network of fine cracks on the surface of a material, for example in a glaze layer. Crazing frequently precedes fracture in some glassy thermoplastic polymers. As it only takes place under tensile stress, the plane of the crazing corresponds to the stress direction. The effect is visibly distinguishable from other types of fine cracking because the crazing region has different refractive indices from surrounding material.
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Crazing in polymers This is a cartoon representation of failure mechanisms in 298x298px Different theories describe how a dispersed rubber phase toughens a polymeric substance; most employ methods of dissipating energy throughout the matrix. These theories include: microcrack theory, shear-yielding theory, multiple-crazing theory, shear band and crazing interaction theory, and more recently those including the effects of critical ligament thickness, critical plastic area, voiding and cavitation, damage competition and others.
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18, (207), 348, 1983."Ways Of Eliminating Glaze Defects In Practice. Pt. 1. Crazing And Peeling".
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As the distance from the tip increase, it tends to thicken gradually with the rate of the increase diminishing with distance. Therefore, the growth of crazing has a critical distance from the tip. The opening angle of the crazing lies between 2° to 10°. The boundary between crazing and surrounding bulk polymer is very sharp, the microstructure of which can be scaled down to 20Å or less, which means it can only be observed by electron microscopy.
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Crazing is also used as a term in odontology to describe fine cracks in the enamel of teeth.
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During the process, the stress applied is negligible, but crazing is still found on the containers. There are many theories that tried to explain the environmental effects upon formation of crazing, among which surface energy reduction and plasticization are widely accepted and well developed. To eliminate the environmental crazing and cracking, many methods like surface coating, stress reduction are adopted. However, due to the complicity of the environmental effects, especially the effects in organic environment, it's hard to find a general solution and remove the effect completely.
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In the three-point bend test, where failure is due to crazing, 2000 nm particles had the most significant toughening effect.
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To specify, yielding happens in the form of crazing or shear band, which can consume a large portion of deformation energy.
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Crazing is also seen on single ply roofing membranes, joint sealant, and on concrete when good concrete practices are not followed.
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Xiangyang Li. Environmental Stress Cracking Resistance of a New Copolymer of Bisphenol-A. Polymer Degradation and Stability. Volume 90, Issue 1, October 2005, Pages 44-52 Research shows that the exposure of polymers to liquid chemicals tends to accelerate the crazing process, initiating crazes at stresses that are much lower than the stress causing crazing in air.J. C. Arnold.
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Glaze defects can be as a result of the incompatibility of the body and the selected glaze, examples including Crazing and Peeling.
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Shear banding is the narrow region with high level of shearing strain from local strain softening; it is also very common during the deformation of thermoplastic materials. One of the main differences between crazing and shear banding is that crazing occurs with an increase in volume, which shear banding does not. This means that under compression, many of these brittle, amorphous polymers will shear band rather than craze, as there is a contraction of volume instead of an increase. In addition, when crazing occurs, one will typically not observe "necking," or concentration of force upon one spot in a material.
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By 1650 the industrial buildings recorded at Trenere Wolas had expanded to a crazing-mill, two stamping-mills and a blowing house.Brooke 1994, pp.
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As with most glazes, crazing (a glaze defect) can occur in the glaze and, if the characteristic is desirable, is referred to as "crackle" glaze.
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In ceramics, craquelure in ceramic glazes, where it is often a desired effect, is called "crackle", or crazing. It is a characteristic of Chinese Ge ware in particular.
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Crazes generally propagate perpendicular to the applied tension. Crazing occurs mostly in amorphous, brittle polymers like polystyrene (PS), acrylic (PMMA), and polycarbonate; it is typified by a whitening of the crazed region. The white colour is caused by light-scattering from the crazes. The production of crazing is a reversible process, after applied compressive stress or elevated temperature (higher than glass transformation temperature), it may disappear and the materials will return to optically homogeneous state.
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Acrylic is susceptible to crazing : a network of fine cracks appears but can be polished to restore optical transparency, removal and polishing typically undergo every 2–3 years for uncoated windows.
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Crazes can be seen because light reflects off the surfaces of the gaps. The gaps are bridged by fine filament called fibrils, which are molecules of the stretched backbone chain. The fibrils are only a few nanometers in diameter, and cannot be seen with a light microscope, but are visible with an electron microscope. The thickness profile of a crazing is like a sewing needle: the very tip of the crazing may be as thin as several atoms.
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The matrix crazing theory focuses on explaining the toughening effects of crazing. Crazes start at the equator where principal strain is highest, propagate perpendicular to the stress, and end when they meet another particle. Crazes with perpendicular fibrils can eventually become a crack if the fibrils break. The volume expansion associated with small crazes distributed through a large volume compared to the small volume of a few large cracks in untoughened polymer accounts for a large fraction of the increase in fracture energy.
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Image shows a fractured surface with voiding.Cavitation is common in epoxy resins and other craze resistant toughened polymers, and is prerequisite to shearing in Izod impact strength testing. During the deformation and fracture of a toughened polymer, cavitation of the strained rubber particles occurs in crazing-prone and non-crazing-prone plastics, including, ABS, PVC, nylon, high impact polystyrene, and CTBN toughened epoxies. Engineers use an energy- balance approach to model how particle size and rubber modulus factors influence material toughness.
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Shear yielding theory is one that, like matrix crazing, can account for a large fraction of the increase in energy absorption of a toughened polymer. Evidence of shear yielding in a toughened polymer can be seen where there is "necking, drawing or orientation hardening." Shear yielding will result if rubber particles act as stress concentrators and initiate volume-expansion through crazing, debonding and cavitation, to halt the formation of cracks. Overlapping stress fields from one particle to its neighbor will contribute to a growing shear-yielding region.
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A material that is expected to fail by crazing is more likely to benefit from larger particles than a shear prone material, which would benefit from a smaller particle. In materials where crazing and yielding are comparable, a bimodal distribution of particle size may be useful for toughening. At fixed rubber concentrations, one can find that an optimal particle size is a function of the entanglement density of the polymer matrix. The neat polymer entanglement densities of PS, SAN, and PMMA are 0.056, 0.093, and 0.127 respectively.
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Figure 1 - Crack-tip Craze ZoneAs metals yield through dislocation motions in the slip planes, polymer yield through either shear yielding or crazing. In shear yielding, molecules move with respect to one another as a critical shear stress is being applied to the system resembling a plastic flow in metals. Yielding through crazing is found in glassy polymers where a tensile load is applied to a highly localized region. High concentration of stress will lead to the formation of fibrils in which molecular chains form aligned sections.
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This haziness is the result of crazing, where fibrils are formed within the material in regions of high hydrostatic stress. The material may go from an ordered appearance to a "crazy" pattern of strain and stretch marks.
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Crazing is a glaze defect of glazed pottery. Characterised as a spider web pattern of cracks penetrating the glaze, it is caused by tensile stresses greater than the glaze is able to withstand.”Ceramics Glaze Technology.” J.R.Taylor, A.C.Bull.
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232x232pxIncreasing the rubber concentration in a nanocomposite decreases the modulus and tensile strength. In one study, looking at PA6-EPDM blend, increasing the concentration of rubber up to 30 percent showed a negative linear relationship with the brittle-tough transition temperature, after which the toughness decreased. This suggests that the toughening effect of adding rubber particles is limited to a critical concentration. This is examined further in a study on PMMA from 1998; using SAXS to analyze crazing density, it was found that crazing density increases and yield stress decreases until the critical point when the relationship flips.
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The coarse gravel or crushed ore was introduced into a hole in the centre of the top stone and was rendered to a fine sand. Only three examples of such crazing mills have been found; at Gobbet mine both stones are still visible.Newman 1998, p.44-45. As it became necessary to regularly process pieces of ore- bearing rock that were too large to be directly ground in a crazing mill, stamping was introduced. This involved vertical hammers powered by a waterwheel in a Stamp mill, of which at least 60 are known to have existed on Dartmoor.
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The root sense of “crazy” in English, meaning “to shatter, crush, or break,” dates to the 1300s. The metaphorical senses familiar today derive from crazing in pottery: “crazy” meaning “diseased or sickly” dates to about 1570; “of unsound mind,” to about 1610.
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PMMA vaporizes to gaseous compounds (including its monomers) upon laser cutting, so a very clean cut is made, and cutting is performed very easily. However, the pulsed lasercutting introduces high internal stresses along the cut edge, which on exposure to solvents produce undesirable "stress-crazing" at the cut edge and several millimetres deep. Even ammonium-based glass-cleaner and almost everything short of soap- and-water produces similar undesirable crazing, sometimes over the entire surface of the cut parts, at great distances from the stressed edge. Annealing the PMMA sheet/parts is therefore an obligatory post-processing step when intending to chemically bond lasercut parts together.
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The rubber chains form separate phases which are 10-20 micrometers in diameter. When the product is stressed, crazing from the particles helps to increase the strength of the polymer. The method of rubber toughening has been used to strengthen other polymers such as PMMA and nylon.
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Crazing occurs in regions of high hydrostatic tension, or in regions of very localized yielding, which leads to the formation of interpenetrating microvoids and small fibrils. If an applied tensile load is sufficient, these bridges elongate and break, causing the microvoids to grow and coalesce; as microvoids coalesce, cracks begin to form.
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The crackles, or "crazing", are caused when the glaze cools and contracts faster than the body, thus having to stretch and ultimately to split, (as seen in the detail at right; see also ). The art historian James Watt comments that the Song dynasty was the first period that viewed crazing as a merit rather than a defect. Moreover, as time went on, the bodies got thinner and thinner, while glazes got thicker, until by the end of the Southern Song the 'green- glaze' was thicker than the body, making it extremely 'fleshy' rather than 'bony,' to use the traditional analogy (see section on Guan ware, below). Too, the glaze tends to drip and pool slightly, leaving it thinner at the top, where the clay peeps through.
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Paper components representing insulation or other lining of the sub-deck are disintegrating. Adhesive mounts and backing for a range of fasteners have become yellowed and embrittled. Delicate plastic components also appear to be degrading slightly. Clear plastic, prismatic ceiling panels have fine crazing cracks, and are starting to become detached at their fasteners.
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Those of earthenware ceramics vary between 3 and 5×10−6/°C for non-calcareous bodies and 5 to 7×10−6/°C for calcareous clays, or those containing 15–25% CaO. Therefore, the thermal contraction of lead glaze matches that of the ceramic more closely than an alkali glaze, rendering it less prone to crazing.
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Feature size changes of the plastic component generally do not occur. Post stress relieving is usually required as vapor polishing sets up surface stresses that can cause crazing. Plastics that respond well to vapor polishing are polycarbonate, acrylic, polysulfone, PEI, and ABS. The technique is also being used to improve the surface of objects created with 3D printing techniques.
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A line of "whiteware" for table use was added. Like most pottery of the time, it was susceptible to "crazing" - small cracks in the glazed surface. The company struggled along until 1871 at which time Onondaga Pottery Company was organized and took over. Popular taste demanded a finer ceramic tableware than the heavy pottery made by these companies.
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There are some general guidelines to follow when trying to determine a plastic's toughness from its chemical structure. Vinyl polymers like polystyrene and styrene-acrylonitrile tend to fail by crazing. They have low crack initiation and propagation energies. Polymers with aromatic backbones, such as polyethylene terephthalate and polycarbonate, tend to fail by shear yielding with high crack initiation energy but low propagation energy.
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Harpalus was the rocket landing site in the 1950s science fiction film Destination Moon. It was chosen by artist Chesley Bonestell as it had a relatively high latitude and the Earth could be realistically displayed at a low altitude during camera shots. However, the resulting clay model depicted crazing (net-like cracks) across the crater floor, an addition to which Bonestell objected.
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In 1512 two local men were overheard quarrelling in Cornish about the theft of "tynne at Poldyth in Wennap". Tin raised in Gwennap was dressed and smelted locally. Early modern 'crazing mills' powered by water, such as that which existed at Penventon, were built to grind, and later stamp the tin ore. This released cassiterite which was then smelted in local 'burning houses'.
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RAAF pre-1953 buttons. (Top left button shows crazing resulting from button having been heated during washing.) Chemical reaction of two proteins (top) with formaldehyde (H2CO) – schematic presentation. Galalith (Erinoid in the United Kingdom) is a synthetic plastic material manufactured by the interaction of casein and formaldehyde. The commercial name is derived from the Greek words gala (milk) and lithos (stone).
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One of the best preserved blowing houses on Dartmoor is above Merrivale Bridge on the River Walkham. It has a mould stone close to its entrance and the wheel-pit can be easily traced. Some blowing houses also housed crushing ("knacking") or grinding ("crazing") mills, and at Gobbet Mine on the River Swincombe both the upper and lower grinding stones were found.
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The former Wheal Lushington engine house in Porthtowan, Cornwall has been converted into a cafe.St Agnes and surrounding farm land from St Agnes Beacon Historically, St Agnes and the surrounding area relied on fishing, farming and mining for copper and tin. There were also iron foundries and an iron works, stamps and crazing mills, a smelter, blowing houses and clay extraction.Cornwall Industrial Settlements Initiative - St Agnes Area.
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Crazing occurs in polymers, because the material is held together by a combination of weaker Van der Waals forces and stronger covalent bonds. Sufficient local stress overcomes the Van der Waals force, allowing a narrow gap. Once the slack is taken out of the backbone chain, covalent bonds holding the chain together hinder further widening of the gap. The gaps in a craze are microscopic in size.
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1973 In pottery a distinction is often made between crazing, as an accidental defect, and "crackle", when the same phenomenon, often strongly accentuated, is produced deliberately. The Chinese in particular enjoyed the random effects of crackle and whereas in Ru ware it seems to have been a tolerated feature of most pieces, but not sought, in Guan ware a strong crackle was a desired effect.
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Surface "crazing" is not restricted to pot boilers - hearth stones and the surrounds of fireplaces may also show the same structure. However, since a pot boiler needs to be manipulated into and out of the fire (typically in anthropological observations, using sticks of green wood) at arm's length, they start off weighing up to several kilogrammes, and shrink by fragmentation ; hearth stones and chimney liners are typically larger.
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The dominant failure mechanism can usually be observed directly using TEM, SEM and light microscopy. If cavitation or crazing is dominant, tensile dilatometry (see dilatometer) can be used to measure the extent of the mechanism by measuring volume strain. However, if multiple dilatational mechanisms are present, it is difficult to measure the separate contributions. Shear yielding is a constant volume process and cannot be measured with tensile dilatometry.
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The breaking away of glaze from ceramic ware in consequence of too high a compression in the glaze layer; this is caused by the glaze being of such a composition that its expansion coefficient is too low to match that of the body. It is the opposite of crazing, as are the preventative steps: see Seger's Rule above. Peeling is also known as shivering."Glazing Faults In Raw Glazes". Ceram. Inf.
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These homemade versions are typically of poor paint quality and may exhibit crazing in the glaze due to poor firing technique.China heads - Antique vs Reproduction Another tip off that such a doll is a reproduction is if it is signed with an individual's name and/or date. The antique dolls were not typically signed in this manner. There were several models of china dolls made in Japan and marketed in the 20th century too.
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In order to gauge the toughening effects of a dispersed secondary phase, it is important to understand the relevant characteristics of the continuous polymer phase. The mechanical failure characteristics of the pure polymeric continuous phase will strongly influence how rubber toughened polymer failure occurs. When a polymer usually fails due to crazing, rubber toughening particles will act as craze initiators. When it fails by shear yielding, the rubber particles will initiate shear bands.
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The body is moulded in high quality glass reinforced plastic. It is extremely tough, non rusting and, being unstressed, is not subject to gel-coat star crazing as found on many cars using GRP body shells. The windscreen is laminated glass and the rear screen perspex. The doors are double skinned glass fibre fitted with anti-burst locks, steel window frames, and steel strengthers to avoid door drop, often found on glass fibre cars.
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Crazing can take place in glassy polymers under environmental effects. It is problematic because it requires a much lower stress state and sometimes happens after a long delay, which means it is hard to detect and avoid. For example, PMMA containers in daily use are quite resistive to humidity and temperature without any visible defects. After machine-washing and left in air for one or two days, they will shutter abruptly when wet with gin.
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Interaction between rubber particles and crazes puts elongation pressures onto the particles in the direction of stress. If this force overcomes the surface adhesion between the rubber and polymer, debonding will occur, thereby diminishing the toughening effect associated with crazing. If the particle is harder, it will be less able to deform, and thus debonding occurs under less stress. This is one reason why dispersed rubbers, below their own glass transition temperature, do not toughen plastics effectively.
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The damage competition theory models the relative contributions of shear yielding and craze failure, when both are present. there are two main assumptions: crazing, microcracks, and cavitation dominate in brittle systems, and shearing dominates in the ductile systems. Systems that are in between brittle and ductile will show a combination of these. The damage competition theory defines the brittle- ductile transition as the point at which the opposite mechanism (shear or yield damage) appears in a system dominated by the other mechanism.
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After being heated in the kiln, the glaze creates its signature fine web of cracks and fine pores -known as kan-nyuu (貫入) or crazing- while cooling. Throughout the heating and cooling process, the cracks form because the glaze shrinks faster than the clay. Over time, a Hagi ware user might notice the color of the glaze getting darker. This is natural as the slightly porous surface absorbs the tea residues or sake through its tiny crackles, maturing over time.
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In ceramics, wollastonite decreases shrinkage and gas evolution during firing, increases green and fired strength, maintains brightness during firing, permits fast firing, and reduces crazing, cracking, and glaze defects. Wollastonite is used in a cement announced in 2019 which "reduces the overall carbon footprint in precast concrete by 70%." In metallurgical applications, wollastonite serves as a flux for welding, a source for calcium oxide, a slag conditioner, and to protect the surface of molten metal during the continuous casting of steel.
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Early streamworkers operating on a small scale used a block of hard stone as a mortar and perhaps a metalbound piece of wood or a ball of stone as a pestle to break up the ore when necessary,Harris 1972, p.28. but the rich gravels would have required little or no crushing before concentration.Newman 1998, p.40. A later technique called "crazing" employed a pair of circular stones used like millstones, the top one rotating on the fixed lower stone.
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An oil painting consists of several layers, comprising the base canvas, a layer of gesso base coat, several layers of the oil-based paint and then several coats of varnish to protect the paint surface. With many different materials, it is understandable that each layer may dry at different rates and will also absorb and release moisture at different rates. When this occurs, expansion and contraction of the painting will result in a crazing of the varnish surface. This pattern of small cracks is known as craquelure.
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Ceramic industry consumes a significant amount of zinc oxide, in particular in ceramic glaze and frit compositions. The relatively high heat capacity, thermal conductivity and high temperature stability of ZnO coupled with a comparatively low coefficient of expansion are desirable properties in the production of ceramics. ZnO affects the melting point and optical properties of the glazes, enamels, and ceramic formulations. Zinc oxide as a low expansion, secondary flux improves the elasticity of glazes by reducing the change in viscosity as a function of temperature and helps prevent crazing and shivering.
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Exposure to a combination of light and humidity changes can cause significant crazing. The amber also has a distinct light absorbance curve that peaks in the ultraviolet B range at 385 nm. This is similar to the slightly older Burmese amber, which has an absorbance peak of 380 nm. Exposure to increase in temperature over a period of time has been shown to result in "yellowing" or darkening of the amber over a long period of time, though not to as significant a degree as seen in Baltic amber.
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Creamware is made from white clays from Dorset and Devonshire combined with an amount of calcined flint. This body is the same as that used for salt-glazed stoneware, but it is fired to a lower temperature (around 800 °C as opposed to 1,100 to 1,200 °C) and glazed with lead to form a cream-coloured earthenware.Donald Towner, Creamware, London: Faber & Faber (1978) , p. 19 The white clays ensured a fine body and the addition of flint improved its resistance to thermal shock during firing, whilst flint added to the glaze helped prevent crazing.
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Headlight restoration or plastic headlight restoration is the act of refinishing aged headlight lenses that have become discolored or dull due to oxidation primarily due to UV light and other environmental factors such as road debris impact (stones, sand, etc.) rain, and exposure to caustic chemicals. Over time the protective hardcoat breaks down with UV degradation and wear from abrasion, etc. If left untreated the headlights will eventually develop small surface cracks, a condition referred to as crazing. The effectiveness of the headlight in terms of light output measured in lux can be significantly reduced.
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Polymers fracture via breaking of inter- and intra molecular bonds; hence, the chemical structure of these materials plays a huge role in increasing strength. For polymers consisting of chains which easily slide past each other, chemical and physical cross linking can be used to increase rigidity and yield strength. In thermoset polymers (thermosetting plastic), disulfide bridges and other covalent cross links give rise to a hard structure which can withstand very high temperatures. These cross-links are particularly helpful in improving tensile strength of materials which contain much free volume prone to crazing, typically glassy brittle polymers.
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In a pre-pottery context, the heating can be done by lining a pit with leather, leaves or clay, and then putting in the water followed by pot boilers directly into the vessel. Such stones can be recognized because the repeated exposure to the heat of the fire followed typically by rapid chilling in water leads to great thermal stress on the stone's fabric due to the thermal expansion and contraction. This typically leads to partial glazing of the stone's surface and a fine network of cracks on the stone's surface (often described as "crazing"). Eventually the stone shatters.
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Although McLeish's work is mostly theoretical, he also works closely with those performing experiments and in industry. He has made significant advances in modelling the structure and properties of complex entangled molecules, blends of substances that don't usually mix (multiphasic liquids like oil and water) see reptation and crazing. This allows us to more easily predict complex fluid behaviour and processing in an industrial setting. Since 2000 he has increasingly worked on biological physics: applying soft matter physics to self-assembly of protein fibrils, protein fluctuation dynamics and its role in allosteric signalling, and statistical mechanics approaches to evolution.
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Although fully mineralized and containing no water—and therefore not subject to dehydration and subsequent crazing as seen in opal—ammolite is often damaged due to environmental exposure. The thin, delicate sheets in which ammolite occurs are also problematic; for these reasons, most material is impregnated with a clear epoxy or other synthetic resin to stabilize the flake-prone ammolite prior to cutting. Although the tessellated cracking cannot be repaired, the epoxy prevents further flaking and helps protect the relatively soft surface from scratching. The impregnation process was developed over a number of years by Korite in partnership with the Alberta Research Council.
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It is therefore thermodynamically inevitable that these metals when exposed to various environments would revert to their state found in nature. Corrosion and corrosion engineering thus involves a study of chemical kinetics, thermodynamics and electrochemistry. Generally related to Metallurgy or Materials Science, corrosion engineering also relates to non-metallics including ceramics, cement, Composite material and conductive materials such as carbon / graphite. Corrosion Engineers often manage other not-strictly- corrosion processes including (but not restricted to) cracking, brittle fracture, crazing, fretting, erosion, and more typically categorized as Infrastructure asset management. In the 1990s, Imperial College London even offered a Master of Science degree entitled "The Corrosion of Engineering Materials".
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The typical choice, poly(methyl methacrylate) (PMMA) is applied to the substrate by a glue-down process in which a precast, high- molecular-weight sheet of PMMA is attached to the plating base on the substrate. The applied photoresist is then milled down to the precise height by a fly cutter prior to pattern transfer by X-ray exposure. Because the layer must be relatively free from stress, this glue-down process is preferred over alternative methods such as casting. Further, the cutting of the PMMA sheet by the fly cutter requires specific operating conditions and tools to avoid introducing any stress and crazing of the photoresist.
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There are five main strengthening mechanisms for metals, each is a method to prevent dislocation motion and propagation, or make it energetically unfavorable for the dislocation to move. For a material that has been strengthened, by some processing method, the amount of force required to start irreversible (plastic) deformation is greater than it was for the original material. In amorphous materials such as polymers, amorphous ceramics (glass), and amorphous metals, the lack of long range order leads to yielding via mechanisms such as brittle fracture, crazing, and shear band formation. In these systems, strengthening mechanisms do not involve dislocations, but rather consist of modifications to the chemical structure and processing of the constituent material.
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When loaded oblique to the chain direction, ductile polymers with flexible linkages, such as oriented polyethylene, are highly prone to shear band formation, so macroscopic structures which place the load parallel to the draw direction would increase strength. Mixing polymers is another method of increasing strength, particularly with materials that show crazing preceding brittle fracture such as atactic polystyrene (APS). For example, by forming a 50/50 mixture of APS with polyphenylene oxide (PPO), this embrittling tendency can be almost completely suppressed, substantially increasing the fracture strength. Interpenetrating polymer networks (IPNs), consisting of interlacing crosslinked polymer networks that are not covalently bonded to one another, can lead to enhanced strength in polymer materials.
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Ge-type vase, with "gold thread and iron wire" double crackle, dated by the Palace Museum Beijing to the Song dynasty Craquelure affecting the glaze in ceramics may develop with age but has also been used as a deliberate decorative effect, which has a long history in Korean and Chinese pottery in particular.Ward, 149 These deliberate glazing effects are usually known as "crackle", with crackle[d] glaze or "crackle porcelain" being common terms. It is typically distinguished from crazing, which is accidental craquelure arising as a glaze defect, although in some cases, experts have difficulty in deciding whether milder effects are deliberate or not.Vainker, 101, 107-108 Some may also only have developed with age.
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Devitrification occurs in glass art during the firing process of fused glass whereby the surface of the glass develops a whitish scum, crazing, or wrinkles instead of a smooth glossy shine, as the molecules in the glass change their structure into that of crystalline solids. While this condition is normally undesired, in glass art it is possible to use devitrification as a deliberate artistic technique. Causes of devitrification, commonly referred to as "devit", can include holding a high temperature for too long, which causes the nucleation of crystals. The presence of foreign residue such as dust on the surface of the glass or inside the kiln prior to firing can provide nucleation points where crystals can propagate easily.
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A plastic item with thirty years of exposure to heat and cold, brake fluid, and sunlight. Notice the discoloration, swelling, and crazing of the material Polymer degradation is a change in the properties—tensile strength, color, shape, or molecular weight—of a polymer or polymer-based product under the influence of one or more environmental factors, such as heat, light, and the presence of certain chemicals, oxygen, and enzymes. This change in properties is often the result of bond breaking in the polymer backbone (chain scission) which may occur at the chain ends or at random positions in the chain. Although such changes are frequently undesirable, in some cases, such as biodegradation and recycling, they may be intended to prevent environmental pollution.
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The body now included bone ash, and a wider range of colours was used, as well as lavish gilding.Spero, 120 The glaze now had a tendency to drip and pool, as well as crazing, and had a slight greenish tint.Lappet, 57 In 1763, George III and Queen Charlotte sent the queen's brother Adolphus Frederick IV, Duke of Mecklenburg-Strelitz a large Chelsea service. This commissioning of porcelain for diplomatic gifts was common among the ruler-owned European factories (and indeed in East Asia), but novel for England. The service was praised by Horace Walpole, who said it cost £1,200, and is now mostly in the Royal Collection, who have 137 pieces.Honey, 66–68; Royal Collection East Asian styles had returned in the red anchor period in the form of versions of Japanese Imari ware, but are more common with the gold anchor.
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The "serpentine" and "stone" of the pillars on this Seth Thomas black mantel clock are made of celluloid glued to wood. Image copyright owned by Mark James Miller Exposure to improper lighting, humidity, water, or solvents may cause chemical deterioration in plastics resulting in reactions such as “a white powder ‘blooming’ on the surface of an object, discoloration, distortion of the object’s shape and strong indicator smells of vinegar, or mothballs,” crazing, cracks, acid deposits, and sticky surface textures. It can be difficult to easily identify the chemical makeup of the plastic used to create an object, which can make interventive conservation challenging because the potential reactions to treatments are unknown. Therefore, preventive conservation tactics similar to those used for organic objects are the primary method of caring for objects made with plastic such as clocks.
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Though the recipe of tin glazes may differ in different sites and periods, the process of the production of tin glazes is similar. Generally speaking, the first step of the production of tin glazes is to mix tin and lead in order to form oxides, which was then added to a glaze matrix (alkali-silicate glaze, for example) and heated.Canby, S. R. 1997 After the mixture cooled, the tin oxide crystallises as what has been mentioned above, therefore generates the so-called white tin-opacified glazes. Besides, the body of tin-opacified wares is generally calcareous clays containing 15-25% CaO, of which the thermal expansion coefficient is close to that of tin glazes, thus avoid crazing during the firing process.Tite, M. S. 1991Ravaglioli, A., A. Keajewski, M. S. Tite, R. R. Burn, P. A. Simpson, and G. C. Bojani. 1996 On the other hand, the calcareous clay fired in an oxidising atmosphere results in a buff colour, thus lower the concentration of tin oxide used Tite, M. S., Freestone, I. and Manson, R.B., "Lead glazes in antiquity - methods of production and reasons for use", archaeometry, 1998, 40:241-260 The white opaque surface makes tin glaze a good base for painted decoration.
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