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Found 10 results

  1. Hi there, I thought someone here may have the answer to this frustrating issue. I have been slip casting and all of a sudden some of these molds started transfering layers of plaster to the porcelain slip after using them for some time. Some of these moulds were a couple of months old some were a couple of years but they all started doing this at the same time. I made new moulds and they started doing the same thing after about 15 casts.They all staretd ddoingit at the smae time again. Loosing fine layers of the plaster onto the porcelain slip cast clay. I have attached some images below both of the moulds and the porcelain with the plaster attached. Also some extra into Also there is no other obvious deterioration of the mould on the outside. Only the small fine layer that has peeled off inside. I am casting a piece a day. It is winter here, but I have a heated studio. I'm using imperial porcelain slip. These moulds I made myself out of potters plaster and are part moulds. I cast very fine works 2-3mm thick They are from different batches of plaster the first and second time. I alowed the moulds to completely dry before using them (no dampness transfered onto newsprint overnight) The moulds that I use plastic clay in are fine! Any ideas? I have asked around a bit in my circle but so far everyone seems perplexed. One thought is that I'm not letting the moulds dry out enough between times. That maybe casting once a day is to much for a plaster mold to take? I' needing to make a lot of work using these designs so I am casting daily and letting the moulds sit over night empty, but it is cold. I'm desperate to keep using them.
  2. From the album Monoprinting with plaster

    Tile I made using a plaster slab, underglazes and porcelain casting slip, learned technique in Andrew Wandless' book 'Image Transfer on Clay' and also Joanne Veevers on CAD. This is still in greenware stage, not entirely sure how all of those colors will look as bisque and then glazed
  3. I am looking to support a biscuit fired lattice structure so i can machine it. I will then need to remove the plaster any advice appreciated. If I enclose it in paster of paris and fire it will the plaster fall away from the fired ceramic if i submerge it in water?
  4. I'm interested in experimenting with alternative porous materials suitable for slip casting, with useful properties such as flexibility, faster drying, increased durability, machinable, etc. Can anyone suggest plastics (foamed PVC, polyurethane, etc.) or other plasters (eg: Hydrostone) worth looking into? Thanks!
  5. Hi guys, I have some pieces I want to cast in plaster for a mould. The pieces will not be particularly flexible and I worry they wont release properly. Its a basic vase shape that narrows in at the top like a pair- this taper part is a 6cm diameter x 8cm long pipe that I feel the plaster will grip too tightly to release and slip out. I haven't had much luck with soft soap and I'm wondering could I rub a candle on my piece to give it a shiny and slightly slippery surface for the plaster to cast? I worry it will ruin the porosity of the mould though. Has anyone done such a thing? Other solutions are welcome but I'm mostly wondering if wax will ruin plaster or there are similar products that wont. Cheers!
  6. Hi All, I have just finished making over 200# of plaster molds for our local Art Center and have come up with a few questions. This is not my first time to make , but with the quantity I made, I seemed to have a variety of different ‘problems’. I actually only ‘lost’ about 5 pieces of 50, so I feel quite successful as I do not work with plaster that often. With your help, perhaps what I perceived as ‘problems’ will not repeat in future mold attempts. For my molds I used new pottery plaster. I weighed out my water and pottery plaster, as directed with my molds, to the ratio of.7 . Plaster was sprinkled over the water and then left to slake for 2 minutes. I then mixed gently from the bottom, getting rid of all lumps. Then I let sit a couple minutes more, gently mixed, and poured it gently into silicone sprayed molds. (Most of the time the plaster settled/slaked under the water but several times not all of the plaster settled so I had extra mixing – I did not notice any difference in my water temps or time – any ideas why it did not settle – plaster set up quickly). I learned that water should be cool rather than warm or it sets too quickly. Several times, altho the plaster was mixed well, as it set in the molds, a thin layer of water formed on top – what did I do wrong? (I just laid a paper towel on the plaster to soak up the water.) Also, twice the plaster did not even get warm - why? But it set up and appears OK. I thumped my molds on the floor after filling to get rid of air bubbles but occasionally I had a few, very small, bubbles show up. They don’t look large enough to cause surface problems in my clay – we’ll see. I have been told to wait to fill the molds until you can draw a finger across the mixed plaster leaving a slight indentation in the mixed plaster surface – is that right? At times it then seemed to set very quickly once I started to pour. I did learn that different brands of silicone release differently. Molds have dried nicely by placing them in the area of our wood burner – can do a lot more at a time rather than in an oven! However they do take about 4 days to dry. Thanks for your comments! They are always appreciated! I learn so much from this forum!!
  7. Hi, I am having problems with some plaster slip- casting molds that I use regularly. I made the molds in March this year and suspect I have cast into each around 30 times. Over the summer they have sat unused for two months in a dry cupboard. I have gone back to use them and I'm finding the casts are now more reluctant to pop out. They seem to be sort of sucked in there and the plaster doesn't want to release the cast. They are five part molds and sometimes just one side seems to stick on, as if it can't take the moisture out of the slip - even if the rest of the cast is relatively dry. The casts will come out in the end but they are taking longer than before and I risk ripping the casts when removing them. Does a mold have an expiry date? Could there be anything I could treat them with? Please help! Thanks, Elle
  8. Hello, This is my first post, so please be gentle I just finished making my first plaster wedging table, and I'm experiencing something odd. No matter how much I sand, scrape, and clean the surface, little specks of plaster are contaminating my clay as soon as it hits. I've attached a photo. As far as I can tell, I followed the instructions for mixing the #1 pottery plaster. I also vibrated the mold to remove bubbles, and I've waited several weeks for it to fully dry. Has anyone ever had this problem? I know I could switch to another surface material, but I've always preferred how the clay moves on plaster, and I cherish it's quick-drying qualities. Any help would be greatly appreciated! Thanks, Matt
  9. Greetings all, I have been making mugs with tiki faces carved in them. I have made molds that have been working so I can reproduce them fairly quickly. The problem is that the molds chip very easily, leaving holes in the mold which then create unwanted that then have to be smoothed out after the pouring and drying. My question is: Is one plaster better or more durable than the others? I have been using pottery plaster #1. However, at my ceramics supply company that I order from I see that they have a number of different types of plaster: Plaster, Hydrocal White with 4500psi compression strength Ceramical Gypsum Cement with 6500psi compressions trength Puritan Pottery Plaster with 2400psi Compression Strength Pottery plaster #1 has a 2000psi compression strength. I'm going to go out on a limb here and guess that the higher the compression strenght, the harder the plaster. If someone could confrim this, that would be great Second question: Who has used a "harder" plaster for mold making and what are the disadvantages or advantages you have found? Still kind of new to the mold making and production process and trying to avoid the years of trial and error, so any information would help a bunch. Thanks, Brian
  10. Hi there, this is my first post on this very helpful site. I can't seem to find much information anywhere about using rubber to make mold masters for recreating slipcast molds. I have been experimenting with making rubber masters of my molds (mostly 2 to 3 piece molds). But I find that whenever I pour a new mold from the master, they don't quite fit together as well as the original. I have experimented with a few different types of rubber, but am limited to products that don't need degassing. Is there any one particular product that is recommended for use in this situation? I've attached a couple of photos to show how I am constructing my masters. The blue handle mold was made using Smooth-on Oomoo 25 (which is very soft), and the light colored one was made using Polytek Polygel 35. Any little tips or tricks would be greatly appreciated. Thanks
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