Document D0RNxgnO4G2m6RKG73D9LwqO

"v a s t e r h a n in g e - UKSETITE IT y Erie Burton ceram. eng. editor rTMr Rtf. Subscription to, or interest in our journal and/or the (lead)solubility of glazes. A2 \ For sane years now, unfortunately the publication of our journal KM/SCC has been postponed. The main reason has been lack of time for editing, be cause of, for the last l-2 years, the editor has been keenly engaged in the study of lead-glaze-solubility and the rise of lead-poisening to the general user of pottery. This problem has been well known for over 2oo years at least, but may be a little more severe today, as we are becoming inoeasingly exposed to lead and similar heavy metals from other sources. With two grandfathers having been doctors, and some observations of the poisoning trough easily soluble lead-boro-silicate-glaze (coloured'.) near at hand, I have found the combined medical and glas structural study of this necessary and worth while. Please let me try to compensate the long waiting for our journal a little, by giving you seme brief information on the subject of my ' research' . Lead-content: In general principal, it appears that one can achieve relative low solubility at any level of lead-content for glazes to be fired above I050 C although it can easily be demonstrated, that one can also find dangerously high solubilities of lead with q^uite low content of lead in the glaze, as well as a high firing-temperature of, say, lloo C. It is against this background, that we have published the enclosed advertisement in the year-book of the Technical Museum in Stockholm, the text of which is -roughly translated: Ceramic glaze: homogenous glasscoating - wishful thinking Phaseseparation means 'different properties side by side' -- one of the reasons for surprising variation in the chemical durability of, for instance, leadbearing glazes. We have -in collaboration with the Swedish Institute for Public Healthinvestigated the lead-solubility of a constant glazecomposition, in which we only altered the content of boric acid (if frit-compositions given by the frit-manufacturers are quite reliable). Prom 0.3 moles B2O3 onwards, we found a sharp increase in the solubility, the rise of which becomes almost vertical between 0.45 and 0.50 mol boric acid (PbO = o*7> Si02 = 2.o). The diagram has the shape of an "S", starting (at 0.3 B2O3) with 1 ppm (^ngPb/liter) and ending at 915 ppm (at 0.82 B2O3). Our preliminary view is, that a soluble second phase (dominantly a borate-glass) starting to form as droplets in a rather stable silicatephate begins to become interconnected when the curve be comes almost vertical. Above the solubility of looo ppm Pb, one begins to approach the absolute leadcontent of the glazed surface, which is in the order of lo 000 mg Pb per square decimeter (50 wt-$ Pb, o.2 mm glaze-layer). The scale of the diagram is logarithmic. Phase separation in glass (glaze) is not an exeption, but almost a regular, at/ least a common phenomenon to be found in very many phase-diagrams of interest /or glazes. However, the significance of this for the safe use of lead (as well as some other hazardous elements) in glaze.s and frits does not seem to have been described in the literature, as far as we are aware. On the other hand is phaseseparation in glasses, at the time beeing, almost the theme most often found in the abstracts dealing with research on glass. please turn over Rinjjvagen 62 Vastcrhauingc Tel 0750 - 210 3S Bunk SVandinavislcj Banken Stockholm Cables Burtonpottcry Stockholm Bankgiro 58-83 00 Pottgiro 50 83 00 LIA-76881 InjMtdUrsfir. -r KM/ Sound. Ceramic CoonnmlcatioDS Ingeni,b, rfoief ^ +i,: '.hi7 .:?' i: 's - Colour in glazes t "Already*1 In 1933 G5UER & CHAEKES wrote ia the Jiw x iig I , of tie American Oeramie Society an "Solubility of Colour;ed Glazes in Organic Acids"*. . In the excellent volume "CKEAKCCS -A Symposium", published^ 1953 by tbs.-Brltiah. Ceramic Society, the paper by A N SMITH "The Structure of Grazes" contains a sentence which I have found most significant, in connection with a review of WEYL's "Coloured Glasses" (a classical monograph): "Colour is due to fields of fccxse that are not fully saturated or balanced, weak binding-forces usually giving rise to strong colours0" If this !: generally oorrect, and vo have found no reason to doubt it, the only conclusion would be to avoid any t large) coloured surfaces in; i d e such pottery which is liable to be in contact with food and drink. For stoneware and hard porcelain with leadless glazes, this, of course, would apply only for any on-giaze-decoration fired on .moseauently, for i<s is rare to find such "enamel"-- colours wliioh are quite free of load, or similar fluxing elements (like bismuth)* Acids in food & drink: Are YOG i-vart, that both animal- and vegetable fat consists of fatty acids? In 31329 SIMEON SEAS la "History of the Staffordshire Potteries" (chapter *Mse and Progress of the Staffs* potteries') wrote: When vessels of this kind are -raployed in either baking or boiling food, it is now ascertained, that tlv- lead glaze is very soluble during the time of heat, and that it intermixed with animal fat, or tbs acid juioes of fruits, or vinegar when cold, and that at is partially soluble even when any of these .remain awhile in xhs vessels cord* ... That fruit acids, as a rule, are bole to dissolve more material from a glaze than, for instance, acetic acid (vinegar', is not always known, nor is it appreciated in wider cixc.les, that just this f'-mily of acids axe almost as effective in a strongly diluted concentration as they are in higher percentage* Many drinks contain seme or ocher acid, without tasting sour at all, for example wine, spirits end coffee often contain soje eaccinio acid* Also carbonic acid can be rather aggressive, and only relative recent glaasresearch. has been able to find the present type of winder,v-gJ.ass-cc rposi ti.an which ijs relatively stable against ins action of tlie very slight carbonic acidity of rain. It is therefore not curprieing, that really meet (alma t all) known oases of poisoning due to soluble lead frcoi glazes have occured in c nneotion with vessels for different types of drink* (There must be many ush^own slighter cases never discovered,:) Besorpinon of lead: lead poisoning as an occupational disease is probably mdat often due to breathing lead-hearir.g dust, white lead, beeing about the greatest risk in thin connection* While ale,0s t all lead taken into the lungs (even as a frit) is -sooner or layer-- beeing absorbed through the effective action of bogy-' fluids which axe very (effective t- dissolve lead in tune t forms, 1t is -as a rule-- k'-en that ingested lead is absorbed only to a surprisingly small degree (lo-2o $}, xhc rest beeing excreted in due course. Vfe have strong evidence, that when lead dissolved by fruit-acids (for example as lead "Citrate) enters the digestive system, it is much more .readily absorbed: People who suffer from lack of stomach-acid (--HCl) , which would be expected to transfer a citrate into chloride -at least partially--, do appear to beccrae more readily jleadpcdaensd. Also Vitamin D-2, "Calciferol", which is known to enable the abs option of calcium by the body, appears to increase the ability for leadabsorption* Unis vitamin depends on ultraviolet light for its formation in fats and milk, for e^rample, which would help explain why the frequency of lead-poisoning is much greater during -the summer-months (see CEISQLM'a paper "Lead Poisoning" in Scientific American, February 1973., where the seasonal pattern of 8_t /, of all lead--poisoning cases ocouring from May through October is brought out most clearly, though only partly explained). Sorry this is becoming longer than I had planned*.* (-3 pages together) please turn over LIA-76882 xn^Mmnrbi 1 rnw-i. ' ( Lead--PoiBoniiig: Volumes could and have `been written about this. Diis need there-- .ft)re not even he an introduction, the only intention is to point out one or two things worth remembering. It is <luite surprising and most satisfactory to find, that almost all the literature I hare studied on lead-poisoning appears to be in fullest agreement about symptoms (and their possible absence) and effects -brain- damage and different forms of paralysis, sterility as well as death beeing the severest-. Also, a high degree of agreement is to be found regarding the maximum daily dose of lead, above which chronic poisoning is liable to occur: -jj mg/day. X could also quote 1 mg lead per day as the 'boarder-line1 from some authors, or even very little more. This depends highly on the rate of absorption, governed by individual differences, as well as on age, sex (the female sex said to be from 1--3 times more vulnerable than the male) and outer factors. Since, according to several irrvestigastions the average human beeing has a "normal" and regular daily inteks of 0.3 (one third.') mg Pb daily /most caning indirectly from the lead in petrol via our food/, it is evident, that there is not much margiri^any addition. I might also point out, that not all doctors are quite familiar with the 'slighter1 symptoms of lead-poisoning, especially in areas where this disease is uncommon as it is nowadays, fortunately. H- TESTING: A German paper from "Sprechsaal fur Keramik, Glas, Unail" of 1873 by Prof. Alex. Schmidt: "Bleiglasur Oder bleifieie Glasur" (=Lead- or Leadless Glaze) gives a most simple but reliable method for a qualitative test. Almost exactly the same procedure was recommended by Gordon BARNES in Tactile, the magazine of the Canadian Guild of Potters, March 197o in his paper: "Lead Glaze Solubility Problem". Gordon Barnes also demonstrated this method during the WOULD CRAFTS CONFERENCE in Dublin, August 197- gcavG a giazed vessel filled with vinegar for about 12 hours. Add a small volume of sulphide-solution. A white precipitate is only colloidal sulphur, liberated If the precipitate is yellow, brown or black,\by the acid, this is due to the presence of lead in the vinegar, the dark compound beeing lead-sulphide. One can easily compare a yellow precipitate with that formed by putting some sulphide-sulution to fresh vinegar, where the cloudy w h i t e precipitate is known to he lead-free. Any water-soluble sulphide vd.ll serve the purpose well. "Liver of sulphur" beeing potassium-sulphide is quite handy, so is sodium-sulphide, and the concentration of the solution is not important, (it's allright if it smells) All the more or less expensive tests give you a figure of your solubility, hut the above test (which can be speeded up by heating the vessel) ought to be known and tried by every potter. The nearest chemist should have the sulphide-salt for you. Different Countries have more or less differing official testing-procedures for glazed utensils. A treatment during 24 hours with 4 % acetic acid is the commonest. The German "lead-law" of I887/88 prescribed the boiling during - hour with 4 % acetic acid (testing as by G.Bames/Prof.Schmidt, above), when "no lead" should have gone into solution. This means less than 3 mg Pb/liter of the solution, and this is the level of the highest permissibbe lead-content according to the Swedish law. Here, however, three -5--hr-boilings are combined, before the dissolved amount of lead is determined, in relation to the volume of the vessel. This procedure has several times been reported to he due to become replaced by the commoner 24-hr at room-temp.-method, hut it was recently decided, that further investigations were necessary, before the method might he changed, since it is by boiling, that the highest figures of solubility are attained. Conferences: In 195^> the "Symposium on Structure and Properties of Glazes", by the British Ceramic Society, was held in Sheffield, 3ee Transactions Vol 55 No lo. 2nd During the 197 Fall Meeting of the American Ceramic Society on October, 197> there was a "Session on LEAD IN GLAZES", reprints of this have been distributed by the Lead Industries Association, Inc., Nw York. The British Ceramic Society arranged a Symposium on "The Solubility Problem in Glazes and Decoration in Stoke-on-Trent on loth Nov. 197o, and a new meeting is due in Hanley on the 16th March, 1972 on "LEAD RELEASE-the present position" HID. LIA-76883