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luca

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About luca

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  1. Yes, there's been some experimentation with wax, and will experiment further with other varieties of wax. The product is intended to be in four colours - white, sandstone, grayish concrete, and black. Beeswax left a yellow cast on the white model, the primary model colour, which was unappealing, but also altered the texture/feel significantly, so even though the colour cast was acceptable on the darker colours, the surface texture was diminished. Unglazed earthenware with a very subtle granular tactile quality is very much the the ideal, target texture. "What you might be wanting is an earthenware glaze that looks like unglazed earthenware." - Indeed. Sufficiently clear and matte sounds to be a problem. Regarding the alumina matte glazes, what was meant by your description of them as having a "harsh hand"...are they extremely rough and textured? And though no ideal glaze for this application comes to mind, are there any mostly clear matte glazes that others can recommend, just for experimentation, and to confirm whether it may work for any the planned colours? Thank you. Kind regards, Luca
  2. Yes, that's correct, experimentation over the preceding year and a half indicates that vitrification is undesirable for our application. Granted, this is not a stark day and night difference (others do use porcelain), however, the low-fire still-porous bodies do outperform porcelain and stoneware, to my ears. The concept also resonates with us on an intuitive/emotional level with our associations to harsh, glassy tones and and materials that embody this. Could anyone suggest, just to get us started, a clear matte glaze suitable for earthenware that they may have had experience and pleasing results with? Kind regards, Luca
  3. John, what a fantastic experience that must have been, working in Kanayama. I've just returned from Kyushu and have been reading up on the influence of Korean pottery in origins of the Japanese pottery industry, and the fascinating history surrounding abducted Korean potters. I'd certainly love to spend a period of time under the tutelage of a Japanese craftsman, in ceramics, or another field....all artists, designers, and craftsman stand to benefit from such high-level commitment to the art that is commonplace in Japan. For this venture, I am largely opposed to the ornamentation of glazing, preferring the 'honesty' of the underlying material, and therefore only necessarily interested in glazes to cope with the issue of oil-absorbency. This is why a clear matte glaze is the focus. I'm very opposed to the slickness of gloss glaze, and the colouring of the material, preferring instead honesty and purity and texture, without any 'barrier' if you will, obstructing touch. As an alternative solution to glazing, some experimentation has been done with firing to maturity once and then coating with a clear petroleum-based solvent-like formula, which is highly transparent and alters the texture of the surface only very minimally. Drawbacks (known thusfar): odour, and moderately effective surface protection. Formulas we're aware of all carry an odour that is unendurable for home interior products, though with time, fades. Bob Zonis, concerning oxides, though the colouring of the exterior is less appealing as mentioned, if no other high-performing solution can be found that meets the specified criteria, then abandoning the colour-in-the-body constraint may be necessary. I've been using oxides in past experiments to colour the earthenware body either sandy tones or grey, with success, but this process surely is different from what you have suggested. How does the oxide wash that you speak of function to seal the porosity and how does burnishing achieve this (or were you suggesting burnishing solely as a means to create texture?) Peter, I'm going through the info in the links supplied (thank you) but let me just first ask directly, can salt glazing be done with earthenware? I should think so, as the pipes you mentioned, are typically a kind of terracotta (earthenware then) no? Parian, on the other hand, would seem to be ruled out as it is a porcelain casting body, thus a high-fire vitrifying body, which won't meet the acoustic requirements. With kind regards, Luca
  4. Firstly, John, yes, I do have concerns about the glaze's effects and durability though they are perhaps not quite like you described. Vibration levels in these rather small units will not be extremely intense, but testing has never before been performed with a glazed earthenware piece (though with glazed stoneware, yes). Any possible flaking, though of course still a negative, is just slightly less a concern given that it would be an entirely clear and very matte glaze, and thus the surface does not differ in colour at all, nor greatly in texture either. My main concern then, is how the glaze may affect sound. It is hoped that it will be minimal/negligible. So for flaking due to vibration and sonic variation caused by the glaze, testing is ahead. Peter, thank you for your input. So I may get a better sense of this, what kind of percentages for shrinkage might typically occur in earthenware for: 1) the first bisque firing (6% or so, for example?) and then... 2) the second firing after glazing (an additional say 3% for a cumulative total of 9%, for example?) and... 3) are the temperatures and time the same for both stages of firing? This assumes firing to maturity in the end. It is hoped that tolerances can be reliably kept within +/- 1% after shrinkage, after the entire process has been tested. I should note that bisqueware tends to perform best sonically, but the body must be fired to maturity for the strength in a functional piece. This leads back to the difficult and opposing constraints that John identified, and for which an ideal technical ceramics solution may exist, however, a level of compromise to the sonic performance may be tolerable – it might be a negligible sonic difference in the end. We'll see. Thanks in advance. Kind regards, Luca
  5. John, the insights and advice are tremendously appreciated. I'll try to refrain from posting further here on topics out of the realm of studio potter's ceramics, but you've taken the time to absorb the length of my posts and have a grasp of the scope of the issues, so thank you for the consideration. At this juncture. it's clear that a turn to a full technical ceramics route could be taken, which I'll continue exploring, but as mentioned, I'm also considering that given the "hit list" is somewhat fulfilled by the current earthenware method, it may be acceptable to carry forward to market with a version 1.0 in earthenware for a limited number of pieces. I expect the advantage to be the chance to gauge user satisfaction and feedback on a wider scale, before moving forward to the technical improvements and innovation that necessitate a new phase of R&D. The main risks entail a possibly more fragile piece than technical ceramics and a problematic surface finish, either totally unglazed and prone to stains, or with a marginally acceptable clear matte glaze. If these prove to be significant, then the risk of damage to product reputation may be too great, I'd be forced to pursue technical ceramics exclusively. I'd hope to gather info on the following, and can post these as separate questions to the community. 1. Suggestions on the use of clear matte glazes (which to try, how to use). 2. How significantly does glaze firing add to the shrinkage of the earthenware piece? I held an incorrect assumption regarding dry pressing, namely that it did not involve firing (and thus avoiding the shrinkage issue, but it ostensibly allows for very precise forming nonetheless). Kind regards, Luca
  6. A description of Pete Pinnell's testing process and findings regarding earthenware can be found here: http://groups.yahoo.com/neo/groups/clayart/conversations/topics/331778 Two brief points concerning the Redart and XX Sagger combination: This is no longer a very low-fire solution (cone 6), and it was mentioned that the pieces, though supposedly falling an impressive 6 feet without shattering, had "a nice ring" to them....which would suggest a level of vitrification takes place, and would not be favourable for my purposes, acoustically. It's why I pursue the more porous less-ringing low-fire clays. Secondly, the colour...sounds like it's not white? A white, as in the examples above, is desired. A sandstone color with mild variagated marks is a second option, but somewhat less preferable. There's no interest on my behalf in pursuing any other colour options. I am not opposed to arranging funding for what will surely be a hugely expensive affair if pursuing hydraulic pressing and the more technical ceramics route, but it would be preferable to go to market, at least initially with a slip casted or perhaps jigger/jolly method produced product, in small volumes. Though I find it very interesting, I would almost prefer to delegate much of this testing and comparing of methods, earthenwares, and processes to someone else. I need to streamline this process, run through it more effectively and efficiently. It's a somewhat unsettling state, knowing rather precisely what the vision is, what's desired and much of what's required, although not how to bring it all together and into being. With all certainty, however, the people and resources are out there to achieve it, to lead one to connect all the various aspects.
  7. Thank you for the replies. John, yes, it's certainly correct to suggest that the distinctions in sonic quality or character would be lost on the general public, however, the design is intended for high-end users and utilizes premium components for a unique product in small scale production, and to carry a price that reflects all of this. The design concept received support for research and development under a UK business incubation program which did involve reviews and focus groups. Continuing with porcelain, as a few others have done in this narrow field, solves the issue of surface stains from handling on the white unglazed body, but the primary reason other groups may gone with porcelain (commonly glazed) was likely due to the assumptions regarding its strength, something which Pete Pinnell's testing has debunked. The low-fired clay bodies offer the key benefits of a level of workability post-firing, and most importantly, a sound that is largely devoid of the more unpleasant glassy resonances found in vitreous materials. Indeed, from a personal standpoint, I cannot get behind such a compromise as those unpleasant resonances in porcelain, particularly for product that is to deliver exceptional performance. Aesthetically, though unglazed white porcelain was attractive and possible to use without picking up hand oils from handling, with earthenware this is not the case. A gloss glaze applied to earthenware largely obscures the material's identity and its unique properties, almost leading one to assume it could be another material (metal, plastics, etc.) that commonly appears in similar products with a perfectly smooth glossy surface. I wish to retain the honesty of the material, such as one would with many woods, where it would be almost criminal to obscure its surface in paint or an opaque glaze. In terms of tolerances, there are cutouts and holes in the piece that need to match up precisely with other components. What advantages do jiggering and jollying provide in this area over continuing with slipcasting? I see how wall thickness can be handled with a more consistent precision in jiggering and jollying, however, it's really in the firing that the variations appear, ones that can require the cutouts and holes to manipulated further post-firing. Moving into the realm of technical ceramics and other forming methods (compression?) may avert this, but then we may lose the warmer aesthetic we desire. To poster MMB, thanks, and are you aware of professor Peter Pinnell's extensive work on the subject of earthenware strength? Is this approach of adding redart and kaolin, claimed, to your knowledge to be reportedly more effective over what Pinnell has found? Perhaps they may work in conjunction. Kind regards, Luca
  8. John, Frederik, and Jim, Thank you so much for your input, which, despite the length of time that has elapsed to this response, have been quite something for consideration. I'm currently based in Taipei, and Taiwan has very strong traditional ceramics culture, as well as being savvy in modern technology with a highly educated populace. The first ceramic engineer (MSc) I've come into contact with here was someone who had worked in the same field of acoustics. To an extent, his exploration in our specific common area began and quickly ended with porcelain, and it's evident we share fundamentally opposing views on the value of different ceramic materials in our application. In his view, any particular ceramic material has a minimal impact on sound, to such an extent that it is entirely insignificant, upon the sonic character of the device. Our opinions diverge not because I do not see the impact on sound as relatively minimal – it can be described as such – but I would not, cannot, go so far as to characterize it as utterly insignificant and undetectable. For him, the impact of the porous nature of earthenware or any other attribute of low fired clay upon sonic performance is nothing more than a distinction without a difference. He's content with porcelain. I counter this with two points: there's something in my subjective experience of listening to identical enclosures made of a porcelain and earthenware in the same environment with the same external equipment, that cannot support his claims, and which he himself does not hear. What humans hear subjectively is not the same as what can be objectively measured, however, it seems the difference is not readily testable with the criteria for measuring sonic performance commonly associated with our device. Testing for frequency response, for example, cannot reveal or convey the qualities of our experience with the materials. Granted, he's fully qualified as ceramics engineer with years of experience, but I come at this from a very different standpoint. My background is in audio, including years of experience mixing and mastering music in a studio environment, and developing audio devices. As a result, we hear differently. As a second point, according the principles associated with emotional design, or kansei engineering, the lack of a quantitative objective difference in performance (which I cannot concede yet) is nevertheless still not grounds for judging the difference in subjective experience as irrelevant. We can be induced into perceiving difference by a variety of means, and the mere perception is in itself, significant for a variety of reasons, from an emotional design standpoint through to marketing, branding, and more. But again, I do not believe the difference is merely illusory. Working down the path developing an optimal ceramic body and forming process in conjunction with a technical ceramics engineer will likely yield the best performing solution, however, there are some additional considerations. Aesthetically, the product would appear to have some characteristics typical of more mass production techniques, and others which place it more in the handcrafted camp. Tolerances must be in the range of +/- 1mm, which by studio production techniques are quite precise, but the surface, the surface texture that is, should be pleasing to the hand and eye, with perhaps some subtle, delicate, mild variations. So the form is quite precise, and must be consistently replicable, but the surface texture, somewhat less so, within limits. An example image will go a long way to convey the intended aesthetic, specifically in terms of colour and surface texture. http://www.aldobakker.com/work/2007/water-carafe/168 http://www.aldobakker.com/work/2005/milk-or-oil-can/114 As this example so captured the intended look and feel of the surface, the designer and Dutch production studio he collaborates with were contacted. The porcelain body they've used was then employed in this prototype, which though perfectly rendering the intended feel (albeit with additional fine texturing applied by sponge on a wheel, adding a subtlety lined whispiness the surface) the porcelain body clearly did not have the sonic properties required: This prototype along with another identical in form but of an bisque fired earthenware were tested fully assembled under identical conditions, with the earthenware sounding much more appropriate. A fundamental issue also is that the surface texture of earthenware looks and feels as desired only in its unglazed state. A clear gloss glaze deprives it of its texture, yet, for white earthenware, a glaze, or perhaps another clear coating of some kind, seems absolutely necessary in order for the piece to be handled without risk of staining by the oils of the hands. In the works above, both by the artist and the prototype, the tighter material structure of porcelain permits handling as an unglazed piece (in its final state) without any real concerns for stains such as one would have in earthenware. If continuing down the studio ceramics route as opposed to the technical ceramics path, and conducting earthenware strenght tests along the lines of what Pete Pinnell has done to determine the ideal body type and firing temperature, along with working out consistent forming and the correct surface texture, if through this 90% of the desired result could still be achieved, then that's acceptable. Material strength will be greater in technical ceramics, but I'm do not wish to lose the connection to a warmer, richer texture product (though not too far in the direction of handcrafts) more typical of studio ceramics. This seems a difficult balancing act, thought perhaps not an impossible one. Apologies for the length, and all thoughts and comments are greatly appreciated. Kind regards, Luca
  9. So earthenware, of the right body and firing procedure, exceeds stoneware's strength in a certain manner – which for my purposes would indeed be fortuitous. I can't help but wonder why the general perception of stonewares among laypeople as offering greater strength persists? Presumably this is related to specific types and measures of strength, i.e. torsional or compressive, in addition to being dependent upon the particular bodies of each clay and its treatment. These particulars will be of great interest to me, and I hope to track these down online. The end goal is understanding in order to arrive at a body and a process which meets my needs for a largely low resonant, non-vitreous still porous body, and strength which surpasses that of, say, terracotta used in pots. Certain forming methods are in, i.e slip casting, which has been used in successful prototypes to date working well, while hand forming is too imprecise. I lack familiarity with other methods but know that control over wall thickness and repeatable results will be quite important. I believe there's a form of press moulding that yields precise wall thickness? I hate to appear to the forum with so many questions at once, however, I have been engaged in informal research and prototyping for well over a year, and have done my utmost to familiarize myself with the world ceramacists (and to an extent ceramic engineers) live in. A recent bit of research involved one of the only published texts on a related field to ceramics and acoustics: ceramic instruments in Barry Hall's "From Mud to Music": http://www.amazon.co...l/dp/1574981390. The author generously agreed to share additional knowledge in a recent phone chat. Close listening to recordings of musicians who perform with these instruments made of various earthen and stonewares, and porcelains, was also informative. What the information in this text and the recordings suggest, are a number of properties which ceramic instruments typically posses and which are enhanced by the their makers' techniques and approaches, can serve as a basis for what to do in my application, though often in precisely the opposite way. For example, ceramic instruments, like non-ceramic ones, need to resonate/vibrate, thus more vitreous ceramics are often chosen. I seek to go in the other direction, reducing resonance. I must come to understand what the specific formulations of eathenware and their process of firing were, which succeeded so well in the tests results described above, and why. Kind regards, Luca Side note: Yixing purple clay, a high fire stoneware, I've found in my readings, is unlike other clays fired in stoneware ranges because it retains a degree of porosity and does not fully vitrify to the extent of most other stonewares at such temperatures. Its still-somewhat porous, non-vitreous body would seem to lend it some of the less ringy tone of eathenware, while retaining strength, but this is based upon the earlier held belief that stoneware generally exceeds eathenware's fired strength, under question now.
  10. Thanks Jim - That's very useful to hear, and would indeed set me down along a different path. With full maturity, just to be clear, this means firing right to a clay's recommended temperature, and not at all over or under, yes? It's really very surprising that Pinnell's tests showed earthenware to come out so strong, almost flying in the face of all assumptions about stoneware strength vs earthenware's, even if this was a function of wall thickness. For my application, wall thickness, unlike in tableware or artistic work, is entirely unrestricted. If the walls must be 1.5 cm thick, or 5/8 of an inch...that's fine. It would be wonderful to hear the whole story of Pinnell's tests - and know, perhaps, just which earthenware clay was used and its firing. I'm searching for it. Earthenware's porosity is key to function in our case - and not due to water absorption or such, but rather, because the porosity contributes somewhat to a more wooden-like (hardwood though) tone. High homogeneity to the body - often desirable among potters - works less well for us, acoustically, it is seems. However, homogeneity would seem to impact strength, which is important. One clay which seem to present model ideal properties is the famous Yixing "purple clay" of china, prized for its special attributes in brewing tea, but significant for our purposes because, as scholars on the subject have noted, Yixing purple clay seems to possess the strength of stronger clays, typically stoneware type clays, along with the porosity of earthenware, valued for absorbing and then transferring the tea leaves flavour. I must learn more about Pinnell's tests. Hope to find more answer! Thank you. Luca, your first assumption is incorrect. Grog weakens the clay body. Grog gives clay strength during throwing and has other benefits but actually weakens the fired clay but only a little and depending on how much grog is used. A year or so ago a well-known potter's, Pete Pinnell, college class tested a lot of clays for strength and his test and others proved that clay strength depends on the clay reaching full maturity, not how high it was fired and Pete's tests even showed that earthenware was stronger than any of the other clays (cone 6, cone 10, etc.) tested. There were some who disputed the earthenware part of the test's accuracy later because of a thickness issue. But, my point here is that grog and other aggregates weaken clay so if you want to make your clay stronger get rid of the grog and other aggregates and fire to full maturity of the clay. Do not depend on what the clay maker claims. You have to test. While you're testing to see where the maturity point is, you could also test other earthenware clays to find a stronger one. Jim
  11. Hello all, I am engaged in a product design venture involving ceramics in an unusual application and must seek out additional expertise of experienced ceramists. Though I'm unable to fully describe the product, I can provide a sense what properties are sought from the ceramic body in order for it to perform its function well, which I'd be very interested in hearing others comment on. To begin with, the fired piece is intended not to ring or resonate such as an instrument would when struck. We've experimented with various clay bodies for this including porcelain, stoneware, and earthenware, experimenting with a range of firing temperatures for each as well as with thicker and thinner walls. The ideal clay body for the application seems to be the low-fire type of clays which do not vitrify, and therefore do not ring in a way that is characteristic of porcelains, and stonewares. Our first concern with earthenware, however, is it's lower strength as compared to other ceramics. I'm aware that the use of aggregates in the clay body ("grog") can strengthen the piece, but have no experience in this matter. It is the first area that I'd hope to gather information on through the forum. What types of aggregates or additives have others here used to successfully increase the strength of slip cast earthenware? I'm keen to hear any tips, no matter how unusual or uncommon, on developing better strength in low-fire clay. Our finished pieces are expected to remain unglazed. All responses appreciated - thank you! Luca
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