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CASTELLÓN (SPAIN) OPTICAL HAZE ON POLISHED PORCELAIN TILES, A CONSUMER'S PERSPECTIVE

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This paper examines the surface effect found on some polished porcelain tiles that has been termed "optical hazing". It is an effect that is considered undesirable by many consumers and it therefore leads to complaints, some of which end up in complex litigation because the effect cannot be seen when the tiles are tested for surface quality according to ISO10545. The effect is sometimes visible on a whole consignment of tiles and sometimes only on a scattering of individual tiles. It is generally only visible in certain types of low angle natural light. Some of the possible causes of the effect are explored and methods for meeting consumers expectations are suggested. A method of reducing and sometimes eliminating the problem on installed tiles is discussed, and recommendations for further investigations into the problem are made. This paper is not a scientific analysis of the cause or causes of optical hazing, rather, it is an examination of a consumer problem in a way that allows the tile manufacturers and sellers to better meet reasonable consumer expectations when supplying one of the most widely used tile formats in the world. 2 CASTELLÓN (SPAIN)
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CASTELLÓN (SPAIN)
1
OPTICAL HAZE ON POLISHED PORCELAIN
TILES, A CONSUMER’S PERSPECTIVE
C. Cass
B. Ed. Dip. T. (Técnico)
Techtile Consulting Pty. Ltd, Sydney, Australia
colin@cass.org
ABSTRACT
This paper examines the surface effect found on some polished porcelain tiles
that has been termed “optical hazing”. It is an effect that is considered undesirable
by many consumers and it therefore leads to complaints, some of which end up in
complex litigation because the effect cannot be seen when the tiles are tested for
surface quality according to ISO10545.
The effect is sometimes visible on a whole consignment of tiles and sometimes
only on a scattering of individual tiles. It is generally only visible in certain types
of low angle natural light.
Some of the possible causes of the effect are explored and methods for meeting
consumers expectations are suggested. A method of reducing and sometimes
eliminating the problem on installed tiles is discussed, and recommendations for
further investigations into the problem are made.
This paper is not a scientific analysis of the cause or causes of optical hazing,
rather, it is an examination of a consumer problem in a way that allows the tile
manufacturers and sellers to better meet reasonable consumer expectations when
supplying one of the most widely used tile formats in the world.
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CASTELLÓN (SPAIN)
1. INTRODUCTION
While the surface effects that are causing consumer complaints are generally
referred to as optical hazing, they take several forms some of which do not fit
comfortably under this title. For the purposes of clarification the following definitions
are used for the most common effects causing complaint.
Optical Hazing: A fuzzy halo seen around certain types of reflected light,
also seen as a milky pattern immediately beside low angle reflected natural light.
Shadowing: Permanent dark smudges only visible on tiles in low angle
reflected natural light
Sealer marks: Regular factory processing marks only visible immediately
beside low angle reflected natural light.
These effects do not photograph readily, and they may appear or disappear
depending on the position from which they are observed, this also makes
measurement of the effects most difficult. Their manifestation may also change
as natural lighting conditions vary. Examples of these effects may be observed in
photos 1 to 6 below.
None of the effects in photos 1 to 6 are visible when the tiles are tested
according to of ISO10545 part 2 section 7 “Surface quality”, that is, from a distance
of 1 metre in 300 lux fluorescent light. In fact, all but the effects seen in photo No.
1 require low angle natural light and they are not generally visible in fluorescent
(or incandescent) light as shown in photo No. 7.
Optical hazing was sometimes associated with cement residues being locked
into the surface of the tiles. However, this is a misdiagnosis as this problem is
more accurately called “grout haze”, and it can usually be addressed by a mild acid
wash which usually fixes the problem. The effects seen on the surface of the tiles
in photos 2 to 6 have not been able to be removed with such acid solutions or by
any other means.
Photo No. 1. The same halogen light reected off 3 different tiles gives 3 different levels of haze
around the light. This is considered to be conventional optical hazing. There are few complaints
about this type of hazing, all the tiles pass the requirements of ISO10545.
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CASTELLÓN (SPAIN)
Photo No. 2. Note the shadow line on the left becomes hazy about half way down.
This localised loss of reectivity is being called optical hazing in the tile industry.
Photo No. 3. The cloudy marks on the tiles in the shaded area typies the complaint being called
“optical hazing” The tiles have a slight travertine vein running east-west the opposite direction to
the hazing.
Photo No. 4. In the same room as photo No. 3 shows a typical complaint of “shadowing”
in the reected light.
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CASTELLÓN (SPAIN)
Photo No. 5. Shows shadows that appear to be consistent with Sousa’s static head
polishing time modelling. 1
Photo No. 6. Shows typical factory applied sealer marks in the central shadow beside
the reected natural light.
The impact on the consumers: The immediate impression on seeing polished
porcelain tiles is that they are hard and glossy. It is reasonable for consumers
to expect that the tiles will have uniform characteristics, that the gloss will be
consistent, that their surface will be blemish free and that the surface will be easy
to maintain and not have marks visible on it that are caused by the manufacturing
process.
Instead, some consumers are presented with tiles that have visible effects
on their surface that lead to complaints. The complaints appear to vary from very
real and valid through to somewhat trivial and invalid. However, there is little
technical information available that can assist in resolving the difference between
the valid and invalid complaints. The author is also not aware of any valid and
reliable methods for measuring the extent of these effects. This makes the setting
of parameters for passing or failing any assessment of the effects arbitrary.
1. F. Sousa, J. Aurich, W. Weingaertner, y O. Alarcon “Analytical determination of the distribution
of polishing time over the surface of polished tiles”. Publicado en el Journal of the American Cera-
mic Society nº90, nov. 2007. pp 3468-3477.
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CASTELLÓN (SPAIN)
While the effects complained about are strictly aesthetic, and they do not
interfere in the physical performance or longevity of the tiles, they do still not meet
the consumer’s expectations. On top of this, there have been legal precedents
set in Australia that make aesthetics an attribute that contributes to “fitness for
purpose”. (McGuffie Vs Wodonga Carpets)
Apart from objecting to regular patterns on the surface that appear to indicate
that something went wrong during the manufacturing process, the most common
complaint is that the tiles cannot be made to look clean. This hits at one of the key
reasons tiles are selected in the first place, that of being easy to clean.
The complaints are often made by persons who expected a mirror like finish
on their tiles, and in some cases this perception was encouraged by sales staff or
manufacturer’s promotion material. When the surface of the tiles is inspected beside
a mirror the reflective values are usually quite similar. An example of a halogen light
reflected off both a mirror and a tile can be seen in photo No. 8. There is a tendency
for sales staff to “over-sell” polished porcelain as a high gloss maintenance free
flooring material leading to consumer expectations being raised to the point where
perfection is expected. This has led to many hundreds of complaints in Australia
with most retailers now developing policies and procedures for handling polished
porcelain reflectance complaints. This includes signs in showrooms, disclaimers on
invoices and brochures explaining optical hazing as an inherent feature of some
tiles. These approaches are likely to have limited legal status and they don’t meet
the primary objective of having satisfied customers. Arbitrators of disputes in these
matters have already found in favour of customers on the grounds that the surface
effects visible are significant enough to warrant replacing the tiles regardless of
whether the standard test passes them as first quality.
Part of the human condition appears to be that when a problem is noticed with
a product it becomes the dominant feature of that product; in this case the effect is
looked for whenever the room is entered. This can lead from simple irritation about
the effects to resentment about the product and those involved with its supply.
Providing clear technical evidence that the tiles meet the international requirements
for first quality tiles, and that the performance characteristics of the tiles are not
impaired in any way does not make the problem go away or become acceptable
to the consumer. The tile industry should probably be adopting a policy of trying
to please all consumers and avoid even the invalid complaints, that is, make tiles
that conform to consumer expectations. Failure to address responsibly the valid
complaints has an adverse impact on the reputation of the tile industry.
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CASTELLÓN (SPAIN)
Photo No. 7. Shows haze around a halogen reection but no haze around a uorescent reection.
Photo No. 8. The halogen down light reects similarly off the polished
tile and the mirror producing haze.
2. GENERAL OBSERVATIONS AND POSSIBLE CAUSES OF
UNWANTED REFLECTANCE EFFECTS
More than 90% of the complaints about surface effects on polished porcelain
are about tiles of Chinese manufacture, though there are occasionally complaints
about European, Middle Eastern and South East Asian product. The tiles are
mostly from double charged pressing, and most complaints are with tiles that
have been “factory sealed”. A huge proportion of polished porcelain tiles used in
Australia are also of Chinese origin, (over 45% of Australia’s tiles are imported
from China, representing about 15 million square metres21) but Chinese tiles are
still dramatically over represented in the complaints.
The lighting conditions in which the effects are visible are specific. The effects
are not readily visible in fluorescent or incandescent lighting, they are usually only
visible in, or directly beside, low angle reflected light from the sky. The more natural
light entering the building the greater the chance the effects will be observed, and
the common architectural feature of floor to ceiling doors and windows found in
2. Tile Today magazine, issue 60 Sept. 2008. pp.18-19 atp@infotile.com.au
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CASTELLÓN (SPAIN)
Australia may be one reason there are so many polished porcelain reflectance
complaints.
With most tile showrooms displaying tiles in artificial light, often fluorescent,
consumers may not be able to see an effect that is later visible in their premises.
To compound the problem further, the problematic tiles are often delivered with
a light wax coating completely covering the surface. This wax is applied at the
factory to protect the tiles while in transit (and to a degree to protect them during
and after laying). This wax means that the surface proper of the tiles is not usually
observed until after the tiles are laid. This usually makes any resolution of a dispute
about the tiles more complicated because now the cost of removing and re-laying
the tiles is involved instead of simply taking the tiles back and issuing a refund.
There is some evidence that shadowing and optical hazing could be a reverse
manifestation of the same effect, although they, are not usually visible in the same
tiles. Photos 3 and 4 show both problems in the one consignment, however, the
complaint is usually one or the other, only occasionally is it both. The tiles in photos
3 & 4 were laid in a unidirectional manner because they had linear pattern in the
double charged layer. (A mock vein cut travertine pattern) The shadowing and
hazing on the tiles seen in photos 3 & 4 were found to always run at 90 degrees to
the pattern in the tiles. This could account for why the undesirable surface effects
on this floor all went in the same direction. The effects often run at 90 degree to
each other where plain coloured tiles have been used.
Many hypotheses have been advanced as to the possible causes of the effects
of shadowing and hazing. Some have now been largely discounted while others are
coming to the fore.
Some considered that most light was directly reflected from the polished
surface, but that some may have penetrated into the mineral components making
up the double charging glaze of particular tiles. It was then thought to refract at
different angles thus causing the effects. This is no longer thought to play any part
in the manifestation of these surface effects.
Possible contributing factors are now believed to be the slightly higher porosity
of the Chinese product, possibly combined with the use of static head polishing
machines. The higher porosity is likely to leave more micro cracks and facets in
the surface of these tiles making them more likely to trap materials that shows up
as stains as well as reflecting light differently. More porous tiles with more micro
cracks also require sealing if they are to perform as well as denser tiles with fewer
micro cracks. This may be a reason that the problems are mostly found on factory
sealed tiles.
The surface gloss of the tiles exhibiting these effects is generally
indistinguishable with tiles that do not exhibit the problem. Measurements taken
with a gloss meter have not been able to discern any difference between areas on
the tiles that have the effects and the areas on the same tiles that don’t exhibit the
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CASTELLÓN (SPAIN)
effects. Gloss meter readings taken from the surface of polished ceramics have
been found by some ceramic scientists to be unreliable, and it appears that there
is currently no acceptable practical means of measuring the surface effects being
complained-of. The application at the factory of certain sealers may complicate the
issue of measuring surface gloss.
The problems could be linked to the polishing procedures used in the factory. The
linear marks associated with “shadowing” that are causing complaint (occasionally
the hazing also takes this linear form) appear to be regularly aligned with the zones
that receive the longest contact with the grinding and polishing stones. (Fickerts)
This feature can be possibly be associated with figure 1 taken from the paper of F.
Sousa, J. Aurich, W. Weingaertner, & O. Alarcon titled “Analytical determination of
the distribution of polishing time over the surface of polished tiles”.3 2
Figure 1. Polishing time modelling for a static head polishing machine.
The above light lines indicating the areas on the surface that have the highest
gloss, equate very closely with the lines of shadowing seen in photo No. 5.
The use of polishing equipment incorporating transverse oscillation (sliding
heads) is now becoming the norm in industry. It is unlikely that this change to sliding
polishing heads will mean reflectance effects no longer happen in a regular and
linear fashion, it may make them more difficult to see, and make their appearance
occur in a less linear way. A model of the length of time that the polishing heads
were in contact with the surface of the tile when transverse oscillation polishing
machines were used can be seen in figure 2 which is from the same paper by
Sousa et al.
3. F. Sousa, J. Aurich, W. Weingaertner, & O. Alarcon titled “Analytical determination of the
distribution of polishing time over the surface of polished tiles” Ib id.
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CASTELLÓN (SPAIN)
Figure 2. Polishing time modelling from a sliding head polishing machine.
That there are parts of the surface of the tiles that receive more grinding
and polishing time can be regarded as probably leading to micro deviations from a
perfectly true or flat surface. Preliminary investigations undertaken at the University
of New South Wales indicated shadowing was related to a 4 to 7 micron deviation
in plane. Obviously, such minor deviations in flatness should not be considered a
defect in the tile. However, this does open up an area of study that could “cast light”
onto the causes of hazing and shadowing on the surface of polished porcelain tiles.
photo No. 9 shows that the perfect grid of the squares in the light box is reflected
with some distortions from the surface of the polished porcelain tiles.43This shows
that the surface of the tiles is not truly flat. Finding regular visual deviations that
coincide with unwanted visual effects on the surface of the tiles would also appear
to be a starting point to see if planarity and the visual effects are linked.
Photo No. 9. The perfect squares on the light box are distorted in their reection off the polished
tiles showing the surface of the tiles is not at.
4. Photo taken in the School of Optometry, University of New South Wales, Australia, with the
assistance of Professor Stephen Dain.
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CASTELLÓN (SPAIN)
This possible link between polishing time and regular effects on the surface
of the tiles should not be confused with the effect seen in photo No. 6 where the
pattern on the surface of the tiles is believed to be related to the mechanical
rotational application (or misapplication) of sealer to the surface of the tiles after
polishing is complete.
It is understood that the bulk of factory sealed tiles coming from China are
sealed using one of two main procedures. In manual or mechanical processes that
are widely described as making the tiles “super glossy” they have either an acrylic
or sometimes a “nano” sealer applied, or they undergo the application of a thermally
cured epoxy sealing process. It is thought to be this latter thermally cured epoxy
sealer that can result in the effects seen in photo No. 6. These marks have until
recently be impossible to remove. They detract from the appearance of the floor
tiling and could be legitimately regarded as an undesirable effect that equates to
a defect. However, once again, when these tiles were assessed according to the
test method set down in ISO 10545 part 2 section 7, none of the defects to be
looked for that are set out in that section were visible and the tiles passed the test
method.
3. AVOIDING CUSTOMER COMPLAINTS REGARDING UNDESIRED
REFLECTANCE PROBLEMS ON THE SURFACE OF POLISHED
PORCELAIN TILES.
Prevention is better than cure, and there are some relatively simple steps
and procedures that can generally prevent tiles that display undesired effects on
their surface from being installed or even being sold in the first place.
It would appear to be incumbent on tile manufacturers and sellers to undertake
actions to prevent consumers being supplied with tiles that are likely to cause
complaint. It is also in their own interest to have satisfied customers. Complaints
related to undesired effects on the surface of polished porcelain tiles should be
able to be detected before the tiles are sold if they are properly inspected.
The first, but most probably most difficult to coordinate step would be for the
tile manufacturers to examine representative samples of their tiles from production
in and beside low angle reflected natural light. This would probably show them
which production runs are likely to cause complaints about hazing problems. In a
recent tour of 4 tile factories in the Foshan district of China it was observed that all
were checking for surface quality under fluorescent light only. If low angle natural
light inspections were undertaken manufacturers could be in a position where they
could declare their tiles to be “haze free” thereby reinforcing market confidence.
The next best procedure would be for tile merchants to remove any transit
wax coating from a representative sample of all new batches of tiles and then
inspect them in lighting conditions where low angle reflected natural light (and some
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CASTELLÓN (SPAIN)
shadow) is available. If undesired effects are visible a plan can be implemented to
address the matter before the tiles are sold.
These inspections, combined with staff training about reflectance issues and
the promotion of the particular characteristics of polished porcelain tiles, should
stop all legitimate complaints.
Some sellers of tiles have tried to get some protection from consumer
complaints by the use of disclaimers and showroom signs alerting customers to
undertake such actions as inspecting their tiles in the lighting conditions prevalent
in their projects before installation. Such procedures may be helpful, but customers
may not have the ability to know what they should be looking for and problematic
tiles could still get laid. Ultimately the responsibility for providing customers with
product that does not cause complaint would appear to rest with the sellers.
Complications have arisen in some cases where a third party is involved in
removing the transit wax after the tiles have been laid. The sellers of the tiles then
maintained that the problems arose from the wax removal processes adopted by
the third party. This may or may not be the case.
Some importers are insisting that the tiles that are supplied to them are
not factory sealed; they then require the tiles to be sealed after laying. This may
address sealer related surface marks that arise in the factory, but it is unlikely to
have any impact upon the problems of shadowing and hazing. This factory sealing
should not be confused with the transit wax. This wax is often applied whether or
not the tiles are sealed at the factory.
Ultimately, the best solution is for the manufacturing process to be modified
so the undesired effects do not appear, but at this stage it is uncertain what causes
the effects, the effects cannot be validly and reliably measured and the effects are
not technically defects. Therefore, fixing this problem at its source may be a slow
process and there are likely to be innumerable complaints before the problems are
eradicated at the factory.
It would appear that it is not the responsibility of consumers or even of well
informed tile installers to undertake wax removal and in-situ reflectance testing of
tiles before installation unless this was a specific instruction from the tile supplier.
Both consumers and tilers need the confidence that the tiles that are to be laid will
not have undesirable surface effects that only appear after the tiles have been laid
and the protective wax removed.
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4. ADDRESSING THE PROBLEM OF UNDESIRED REFLECTANCE
PROBLEMS ON TILES THAT HAVE ALREADY BEEN INSTALLED
From when the first complaints were received about reflectance effects on the
surface of some tiles, attempts have been made to remove those effects. Dozens of
different products and processes were used to try and strip, or clean, or seal or re-
polish the tiles, without success. Varying degrees of success were achieved on the
epoxy sealer marks using a hot burnishing technique, but the improvements were
not always permanent and the marks sometimes came back when the tiles cooled.
However, very recently, a methodology that involves chemically removing some of the
gloss from the tiles, then restoring that loss of gloss with synthetic diamond polishing
has been shown to dramatically reduce or completely remove the complained-of
effects. This process is slow and expensive but it is still far cheaper, quicker and more
environmentally friendly than removing the floor tiles and replacing them.
An example of a shadowing problem before and after the de-glossing and re-
glossing treatment can be seen in photos 10 & 11.
A flow chart has also been developed which sets out a recommended procedure
for handling consumer complaints about polished porcelain reflectance effects.
Photo No. 10. Shadowing on a oor in Sydney before treatment.
Photo No. 11. The same area after de-glossing and re-glossing treatment. Note only the 4 tiles out
from the doorway were treated as a test to meet customer satisfaction.
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CASTELLÓN (SPAIN)
5. CONCLUSIONS
It is understood that manufacturers, importers and retailers of polished
porcelain tiles have an obligation and a desire to satisfy customer expectations.
However, there has been a spate of complaints about undesirable surface effects
on this type of tile in Australia recently and complaints have also been lodged in
the UK.
The effects falling under the descriptions of “Optical hazing”, “Shadowing”
and “Sealer marks” are real. They occur almost exclusively in tiles of Chinese
manufacture. The effects are sometimes difficult to see and are only visible in
certain lighting conditions. The severity of the effects can range from trivial through
to readily visible and equating to a defect Sometimes there are only a few tiles
affected but usually there are many, sometimes the area where the effects are
visible are relatively small and other times the area is large.
However, even in cases where the effects are obviously a manufacturing
defect, the tiles meet the requirements for establishing surface quality set down in
ISO 10545 part 2 section 7 because the viewing angle and the lighting requirements
does not allow these effects to become observable. The list of defects that are noted
in the ISO test method currently does not include haze or reflective characteristics
of the surface of tiles.
There are several possible causes of the different manifestations that are
causing complaint about the marks on the surface of some polished porcelain tiles.
It has not yet been established exactly what causes the undesirable effects though
thermally cured epoxy sealer is closely linked to one problem and tile surface
geometry is possibly linked to shadowing and optical hazing. More technical and
scientific studies into the causes appear justified if consumers are to be offered
reasonable protection from polished porcelain tiles that display unwanted surface
effects.
A problem also arises because there appears to currently be no objective
way to measure or quantify these surface effects that are only visible in or beside
low angle reflected natural light. The gloss meters, which have been shown to
be valid and reliable in the paint and auto industries, are apparently not capable
of discerning the marks that are causing complaint on the surface of polished
porcelain tiles.
Under these circumstances, there appears little to protect consumers,
sellers or manufacturers of polished porcelain tiles that exhibit these unwanted
characteristics. But in the end, consumer protection legislation, along with consumer
buying habits are likely to win out, and the tile industry has a problem which it
needs to address. Eventually, there is likely to be some definitive standards and
tests which will set allowable limits for the effects seen, but this is likely to be many
years off.
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CASTELLÓN (SPAIN)
In the end these unwanted surface effects are negatively impacting upon the
image of polished porcelain tiles in the market place and it has led to profound
dissatisfaction particularly when customers are advised their tiles are first quality
and that technically the effects are not faults.
Fortunately, in the short term, careful inspection of a representative sample
of the tiles in and beside a natural low angle light source should be able to identify
tiles with these surface problems and stop them from being sold. This action should
be accompanied by sales staff training and selling procedures that develop a close
match between consumer expectations and tile performance.
For those cases where the problem has been complicated by the tiles being
laid before the undesirable effects were noticed, then there is now a de-glossing
and re-glossing procedure available that should address consumer complaints
without the necessity to remove and replace tiles.
Eventually, these surface reflectance problems need to be addressed by the
manufacturers and this will only occur if there are suitable scientific and technical
studies undertaken by those associated with the industry.
6. RECOMMENDATIONS
Currently, the best method of avoiding consumer dissatisfaction because of
the appearance of unwanted aesthetic surface effects on polished porcelain tiles is
for systems of product inspection to be implemented.
Manufacturers, importers and sellers of polished porcelain tiles, particularly
those emanating from China, should undertake routine inspections of representative
samples of their products to ensure they do not exhibit the undesirable surface
effects that are only visible in or beside low angle reflected natural light. This is
likely to involve the removal of the thin wax coating applied over the surface of the
tiles to protect them in transit.
Sellers of these tiles should implement some training and procedures to
increase the likelihood that the performance and appearance of the tiles sold
closely match the expectations of consumers.
If sellers of tiles that display these unwanted effects are found in a position
where the tiles have already been laid and their customers are complaining, they
should consider becoming involved with the treatment of the tiles with a de-glossing
and re-glossing treatment currently only offered by one company in Australia.
In the longer term, the solution to this problem lies in altering the manufacturing
processes that cause it. It would appear that the ceramic tile industry, particularly
the Chinese manufacturers involved in the production of polished porcelain tiles,
would benefit from technical and scientific studies that establish the cause or
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CASTELLÓN (SPAIN)
causes of optical hazing, shadowing and sealer marks on polished tiles.
Studies that could possibly be considered are:
• Methodologies for the identification and measuring of surface effect s on
polished porcelain tiles that are only visible in or beside low angle reflected
natural light.
• Determining if the planarity of thesur faceof polished porcelain tilesis a
factor in the appearance of optical hazing or shadowing only visible in or
beside low angle reflected natural light.
• The effects of various light types and sources on the observability of
unwanted surface effects on polished porcelain tiles.
• Theimpactofsintering,poro sityorpolishingproceduresontheappearance
of unwanted visual effects on polished porcelain tiles when viewed in or
beside low angle reflected natural light.
• Determiningtheimpactthatvarioustypesoffac toryappliedsealerhaveon
the appearance of unwanted surface effects on polished porcelain tiles.
• Thelongtermeff icacyofthevarioustypesoffactoryappliedsealers.
Once conclusive results from studies such as those listed above are available
then ISO Technical Committee 189 may possibly be able to consider expanding the
test methods for surface quality to include reflectance characteristics when it is
reviewing the content of the international standards relating to ceramic tiles.
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[7] Surface porosity of polished glazes, certain variables. A. Escardino, J. Amoros,
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347 7.
... The kinematics adopted in the polishing train is a key feature for defining the final glossiness pattern to be expected over the surface of polished tiles [1]. Each polishing train offers a continuous spectrum of kinematic possibilities, according to the set of different motions available. ...
... Both forward and transverse oscillation motions are accomplished at the same time, so that each polishing head performs a sinusoidal trajectory relative to the tile surface. As result, an undesired zigzag pattern of glossiness, known as "polishing shadows", are sometime observed on polished surfaces [1]. However, due to the fixed alignment of the tiles on the conveyer belt, the variability of gloss tends to be more intense along the polishing direction (defined by the forward motion). ...
Article
This work evaluates a new kinematics for the industrial polishing process of porcelain stoneware tile. In addition to the typical motions available in industrial polishing trains, each ceramic tile undergoes a discrete rotation during the polishing process, so that more uniform gloss distributions can be obtained without radical changes in the industries facilities. The consequences of this alternative were quantitatively analyzed. A customized computer numeric control (CNC)-machine was used for obtaining the corresponding experimental results. A reasonable linear correlation between theoretical and experimental gains in uniformity was verified, making viable the use of computational simulations to assist the on-line decisions during the tile production.
... The literature is able to offer many fruitful results about the polishing process of porcelain stoneware tiles produced with the usual raw materials. Most of those investigations are focused on optimizations of production parameters, such as kinematics (Sousa et al., 2010), abrasive sequence (Hutchings et al., 2005;2006), surface inspection (Soares Filho et al., 2017), and others phenomenological aspects of the polishing process of commercial compositions of porcelain stoneware tiles (Nascimento and Sousa, 2014;Sousa et al., 2014), as well as the examination of the polishing final quality with the consumer view (Cass, 2010). ...
Article
The industrial production of bricks and roof tiles plays a significant role in the economy of the state of Rio Grande do Norte, in northeastern Brazil. In the last years, production has grown exponentially, and so has the production of the waste from the breakage of those materials. Consequently, the concern has also arisen over the final disposal and reuse of this waste. Several studies reported the incorporation of this waste in the ceramic tiles matrix for porcelain stoneware tile, but only focused on the evaluation of basic technological properties. The present work investigates the influence of this waste over the gloss-gaining curve of the final products. The polishing behavior of three different eco-friendly compositions, with 5, 10 and 15% of waste from the breakage of bricks and roof tiles incorporated, was evaluated in comparison with standard composition, waste-free. For this purpose, porcelain stoneware tile samples were prepared and their corresponding microstructures were characterized. The industrial polishing condition was reproduced on a laboratory scale, keeping the same abrasive agent, SiC, in an automatic metallographic polishing machine. The roughness and gloss performances through the abrasive sequence adopted were investigated. Additionally, the texture of the surfaces was also evaluated. The results show a positive influence of the microstructure caused by the waste on the polishing performance, reaching a maximum of 72.7 gloss units for the composition with 15% of waste incorporated, representing an improvement of 13.7 gloss units comparing to the waste-free composition. Furthermore, the investigation indicates the feasibility and the promising potential of the polishing process of formulations containing this waste as an alternative raw material.
Article
The present work addresses the distribution of texture over the surface of porcelain stoneware tiles due to kinematics imposed by industrial polishing process. The scratching process was simulated using a computational algorithm, which was based on the kinematic equations for the whole myriad of abrasive particles. Different scratching patterns were identified over the polished surface and their corresponding positions were mapped. The experimental results showed that regions in the tile centre present smaller tendencies for exhibiting preferential textures than those of the lateral ones. The final texture was slightly asymmetric and different from those simply left by the last scratches. The definition of three polishing domains was then suggested according to different phenomenological criteria. Results from both experiments and simulations made evident the influence of the kinematic parameters adopted by the industries on the polishing quality of porcelain stoneware tiles.
Article
Several kinds of glossiness pattern can be seen on the surface of porcelain stoneware tiles right after the polishing process, as a function of the kinematics performed by the polishing heads. For the newest generation of industrial polishing trains, where a transverse oscillation is included, there is still a great need for literature about the resulting patterns. This paper intends to find the spatial distribution of time under polishing analytically using the kinematics equations involved in the polishing process. The measured values of glossiness collected from three polished tiles are also presented. The importance of adopting a good kinematics for the polishing process has been highlighted, and the equations developed herein are useful tools for further attempts at optimizing the polishing process.
  • E Sánchez
  • M J Ibáñez
  • J García-Ten
  • M F Quereda
  • I M Hutchings
Porcelain tile microstructure: Implications for polished tile properties E. Sánchez, M.J. Ibáñez, J. García-Ten, M.F. Quereda, I.M. Hutchings and Y.M. Xu Journal of the European Ceramic Society No. 26. 2006.
Modelling of the industrial ceramic tile polishing operation
  • V Cantevella
  • E Sanchez
  • M J Ibáñez
  • J García-Ten
  • J Sanchez
  • G Soler
  • J Sales
  • F Mulet
  • S Mor
  • Qualicer
Modelling of the industrial ceramic tile polishing operation. V. Cantevella, E. Sanchez, M.J. Ibáñez, J. García-Ten, J. Sanchez, G. Soler, J. Sales, F. Mulet, S. Mor. Qualicer 2006.
  • I M Hutchings
  • Y Xu
  • M Ibáñez
  • M Quereda
I.M.Hutchings, Y. Xu, M, Ibáñez, M. Quereda. Journal of Material Science No. 40 2005 p37-42.
Surface porosity of polished glazes, certain variables
  • A Escardino
  • J Amoros
  • M J Orts
  • A Gozalbo
  • S Mestre
  • J Aparisi
  • F Ernando
  • L Sanchez
  • Qualicer
Surface porosity of polished glazes, certain variables. A. Escardino, J. Amoros, M.J.Orts, A. Gozalbo, S. Mestre, J. Aparisi, F. Ernando, L. Sanchez. Qualicer 2002.