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Original Message "Lime versus Gypsum for Fresco" Posted by Ilia on 25-Mar-01 at 00:20 AM >Stale beer >was actually added to lime >plaster as a "sizing" agent >- this would be similar >to adding gum arabic, it >acts like a glue, helping >it stick to walls and >also forming a "skin" on >the surface to make sure >the gypsum is properly hydrated. > > Hi Gary! I hope you do not mind, but I had to clarify this, about the gypsum. It might be confusing. Gypsum plasters are used for ornamentation elements and such. Gypsum is a big enemy of the fresco, fresco plaster should contain nothing but lime putty and sand (or sand and marble dust, volcanic "sand"). Fresco needs calcium oxide not calcium sulfate. Lime, in Italian called "calce" - calcium. GYPSUM - : a widely distributed mineral consisting of hydrous calcium sulfate that is used esp. as a soil amendment and in making plaster of paris. sulfates - : a salt or ester of sulfuric acid salt is a death sentence for fresco. LIME - : a caustic highly infusible solid that consists of calcium oxide often together with magnesium oxide, that is obtained by calcining forms of calcium carbonate (as shells or limestone), and that is used in building (as in mortar and plaster) and in agriculture -- called also quicklime. For fresco we should look for lime without magnesium (causes fluorescence and weakens the plaster. Ilia Anossov fresco painter, sculptor http://www.truefresco.com/workshop >Another possible purpose to tasting the >plaster is that sugar may >have been added to the >lime. For some reason sugar >causes the lime to accept >up 14 times more water >- at the price of >substantially weakening it at this >high level. This would not >be an issue with me >and my home made, high >calcite lime putty, but if >you were ordering the "white >gold" putty from Europe, you >may want to check if >it has been sugared/extended by >tasting, but I doubt that >any company would risk its >reputation with this trick. This is a good thing to now! Thanks for the advice. Here goes my stomach!!!

Go back     FAQ       Conferences Post form Your Message Name*: Subject*: Message*:   HTML Ok Use [] in place of <> HTML Reference   Images Ok   Click on a smilie to add it to your message.   >>Stale beer >>was actually added to lime >>plaster as a "sizing" agent >>- this would be similar >>to adding gum arabic, it >>acts like a glue, helping >>it stick to walls and >>also forming a "skin" on >>the surface to make sure >>the gypsum is properly hydrated. >> >> >Hi Gary! > >I hope you do not mind, but I had to clarify >this, about the gypsum. It might be confusing. > >Gypsum plasters are used for ornamentation >elements and such. > >Gypsum is a big enemy of the fresco, fresco >plaster should contain nothing but lime putty >and sand (or sand and marble dust, volcanic >"sand"). Fresco needs calcium oxide not calcium >sulfate. Lime, in Italian called "calce" - >calcium. > >GYPSUM - : a widely distributed mineral >consisting of hydrous calcium [b]sulfate[/b] >that is used esp. as a soil amendment and in >making plaster of paris. > >[i]sulfates[/i] - : [b]a salt[/b] or ester of >sulfuric acid >[b]salt is a death[/b] sentence for fresco. > > >LIME - : a caustic highly infusible solid that >consists of calcium oxide often together with >magnesium oxide, that is obtained by calcining >forms of calcium carbonate (as shells or >limestone), and that is used in building (as in >mortar and plaster) and in agriculture -- called >also quicklime. > >For fresco we should look for lime without >magnesium (causes fluorescence and weakens the >plaster. > >Ilia Anossov >fresco painter, sculptor >http://www.truefresco.com/workshop > >>Another possible purpose to tasting the >>plaster is that sugar may >>have been added to the >>lime. For some reason sugar >>causes the lime to accept >>up 14 times more water >>- at the price of >>substantially weakening it at this >>high level. This would not >>be an issue with me >>and my home made, high >>calcite lime putty, but if >>you were ordering the "white >>gold" putty from Europe, you >>may want to check if >>it has been sugared/extended by >>tasting, but I doubt that >>any company would risk its >>reputation with this trick. > >This is a good thing to now! Thanks for the >advice. Here goes my stomach!!! Check if you DO NOT wish to use emotion icons in your message

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