giorgiodidon Posted September 18, 2023 Report Share Posted September 18, 2023 (edited) hi all, i'm having some problems with slip casting, as you can see after 25 minutes my pieces are very defectives, i cannot figure out with this issue. the slip respect water ratio given (it is pc010b porcelain, should be 4,1 liter per kg porcelain) and works well in small one piece mold (espresso cup dimension). the photos shows a water glass 2 pieces mold. thank you for your time giorgio Edited December 8, 2023 by giorgiodidon Quote Link to comment Share on other sites More sharing options...
PeterH Posted September 18, 2023 Report Share Posted September 18, 2023 (edited) 2 hours ago, giorgiodidon said: hi all, i'm having some problems with slip casting, as you can see after 25 minutes my pieces are very defectives, i cannot figure out with this issue. the slip respect water ratio given (it is pc010b porcelain, should be 4,1 liter per kg porcelain) and works well in small one piece mold (espresso cup dimension). the photos shows a water glass 2 pieces mold. Can you confirm your slip recipe. Potterycrafts gives 18.5 litre of water to 50 Kg powdered clay (i.e. 0.37 litre water to 1 Kg powdered clay). https://www.potterycrafts.co.uk/Products/pottery-powdered-clays/P3103 Walkers give 9 to 12 litres water to 25 Kg powdered clay (i.e. 0.36 to 0.48 litres of water to 1 Kg powdered clay) https://shop.walkerceramics.com.au/AW500.B/Limoges-PC010B(CM10)-Porcelain-~25kg/pd.php Can you confirm that you didn't use freshly-made casting slip, as it takes a while to fully hydrate the clay (e.g. overnight). Edited September 18, 2023 by PeterH Quote Link to comment Share on other sites More sharing options...
giorgiodidon Posted September 18, 2023 Author Report Share Posted September 18, 2023 (edited) Hi Peter, did not find this water ratio thank you, I will try 0.36 liter per kg. Do you think too much water in my slip could gives these problems? Edited September 18, 2023 by giorgiodidon Quote Link to comment Share on other sites More sharing options...
giorgiodidon Posted September 18, 2023 Author Report Share Posted September 18, 2023 I will try also waiting 1 or 2 days to fully hydrate slip Thank you Quote Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted September 18, 2023 Report Share Posted September 18, 2023 Yup, wrong ratio from somewhere. I am amazed you get anything to cast using 10x more water than normal. Quote Link to comment Share on other sites More sharing options...
giorgiodidon Posted September 18, 2023 Author Report Share Posted September 18, 2023 I apologise, my ratio was 0.41 liter per kg, I'm sorry!! Quote Link to comment Share on other sites More sharing options...
PeterH Posted September 19, 2023 Report Share Posted September 19, 2023 I'd hoped that one of the experts would have commented by now. Looking your pictures. Is the one on the left a casting of the water glass, and the one on the right a casting of the espresso cup? Do you have any idea why the two surfaces look so different. Did you do anything differently when making the casts or the moulds. Looking at the first picture. The inside is very uneven and I've no idea why, so I'll just mention a few possibilities ... Defective slip? - Was the slip nice and uniformly smooth: as it went into the mould and as it came out. No lumps or uneven "thickness" or jelling. Defective mould? - Did you buy it or make it yourself. Defective plaster? - What plaster did you use, and what was the ratio of plaster to water Contaminated surface? - Did you use a parting agent when you cast the mould. Damp mould? - How did you dry the mould after making it. How long did you dry it for. Outside OK? - Can you confirm that the outside of the casting is smooth and uniform. PS I wouldn't change your slip until you have some idea why the two castings came out so very differently. Quote Link to comment Share on other sites More sharing options...
Min Posted September 19, 2023 Report Share Posted September 19, 2023 @giorgiodidon, did you check the weight of the slips against the chart that is available for those slips? From one of the links that Peter linked: https://shop.walkerceramics.com.au/documents/sr/WC-AW500-SR.pdf Do you have a Ford cup (or something equivalent to those) to measure viscosity / fluidity? Did you add any additional deflocculants? I've never mixed a slip where the deflocculants are included in the mix, @Jeff Longtin, could this be the issue? I'm seeing a greenish film inside the lumpy casting, floc issue? Quote Link to comment Share on other sites More sharing options...
PeterH Posted September 20, 2023 Report Share Posted September 20, 2023 5 hours ago, Min said: Did you add any additional deflocculants? I've never mixed a slip where the deflocculants are included in the mix, https://www.potterycrafts.co.uk/Products/pottery-powdered-clays/P3103 Deflocculants are added in the spray drying of this clay so it is not necessary to add them. Quote Link to comment Share on other sites More sharing options...
giorgiodidon Posted September 20, 2023 Author Report Share Posted September 20, 2023 Hi all, both photos same thing, I have tried with 2 water porcelain ratio first 0.41 liter per kg and also 0.39 liter per kg, settled for 2 days and sieved. I think at this point that the problem is in mold, It is an Italian plaster I used 1 to 1 water plaster ratio, and used soap for demolding. I noticed that bumps in the pieces are the same in every piece, so it must be a mold issue. I made a mold 70 water 100 plaster but it is too thick, pouring very difficult, I'll try with some more water (waiting mold dry) Giorgio Quote Link to comment Share on other sites More sharing options...
Min Posted September 20, 2023 Report Share Posted September 20, 2023 4 hours ago, PeterH said: https://www.potterycrafts.co.uk/Products/pottery-powdered-clays/P3103 Deflocculants are added in the spray drying of this clay so it is not necessary to add them. Yup, I read that too, the other link has a link to the one I posted above (slip recipe) and has Dispex at 1 - 12.5 grams per 25kg of dry mix. For sure the plaster needs to be mixed at the correct water:plaster ratio. Quote Link to comment Share on other sites More sharing options...
Jeff Longtin Posted September 21, 2023 Report Share Posted September 21, 2023 A couple things: plaster - if mixing 70-100 results in a thick mixture, and you only mix for 2-3 minutes, its likely you have old plaster. Adding more water helps with the pour but it will result in soft plaster. (Also takes longer to set up.) New plaster would be a good start. slip - If you don't know if, or what, deflocculant was added to the clay before you purchased it, it may be best to first attempt to make a slip with a decent flow. Add enough water to get a decent flow and let the mix sit overnight. See how much it thickens overnight. In the morning add some more water if it needs it. Its been my experience that if the slip is over deflocculated it will gel up in the mold no matter how thin you mix it. If the slip has too much water you will mostly get an extremely thin casting. I've never gotten a lumpy pour with too much water. Lumpiness is mostly a case of deflocculation issues. Mold soap - did you allow the soap to dry before pouring the plaster? If it was still wet it could seal the surface of the plaster and slow the absorption of water. Laguna Clay sells their B-mix in a powder form in a "Casting" version. They list the recipe on their website. What their website does not indicate is that the "Casting" version also contains the dry form deflocculants, soda ash and barium, already mixed into the dry powder. giorgiodidon and PeterH 2 Quote Link to comment Share on other sites More sharing options...
giorgiodidon Posted December 8, 2023 Author Report Share Posted December 8, 2023 thank you all for answers, after all, it was a soap problem i thought it was dry, but in some ways it sealed surface, solved using a wet sponge cleaning the surface! it works well giorgio Min and Jeff Longtin 2 Quote Link to comment Share on other sites More sharing options...
PeterH Posted December 9, 2023 Report Share Posted December 9, 2023 On 12/8/2023 at 9:58 AM, giorgiodidon said: thank you all for answers, after all, it was a soap problem i thought it was dry, but in some ways it sealed surface, solved using a wet sponge cleaning the surface! it works well giorgio What were you using the soap for? Soap reacts chemically with plaster to form insoluble "soap scum". Used correctly this is an effective way to seal a plaster master, but you don't want to let the soap react with your plaster mould. What is Potter's Soap, and how do you use it? https://www.artcoinc.com/potterssoap.php Quote Link to comment Share on other sites More sharing options...
Jeff Longtin Posted December 13, 2023 Report Share Posted December 13, 2023 When I was a young mold maker I read every mold making book I could find. Most were British and oriented toward "factory" methods. (And all referred to molds as "moulds".) Out of all the books I found only one mentioned leaving the mold soap wet while you poured. So I tried it. The results were terrible. (Like the results Giorgio had.) Afterwards I decided to wait until the mold soap was completely dry before pouring. If memory serves me right none off the books actually said, "wait until the soap dries." They all talked about using it but none actually discussed its usage in actual practice. Quote Link to comment Share on other sites More sharing options...
PeterH Posted December 13, 2023 Report Share Posted December 13, 2023 3 hours ago, Jeff Longtin said: (And all referred to molds as "moulds".) Well it is the UK spelling. Chilly and Jeff Longtin 2 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.