Use and Measure Mugs
The real question is how do you get hot liquid from a table into your mouth and make it an enjoyable experience. I think the best mug is a tool that becomes an extension of your hand. To figure out which design aspects we want to consider we used mugs… lots of mugs made by a lot of different people. The questions that we decided were important were:
- How much does it hold?
- How does it sit on a table?
- What is the opening so that the hot liquid flows into your mouth and you dont hit your nose?
- Does it fit in your hand when you hold it?
- What is the weight?
- Where does the handle go?
- How many fingers fit in the handle to get the proper torque with a full mug of liquid?
- How far out should the handle go so you dont burn your fingers?
- Where does the handle fit in your fingers when you hold it?
- How can we embellish the form to make it more interesting once it is dimensioned?
Sketch and Dimension prototypes
We start with initial sketches by finding the starting dimensions we want for the foot and the lip. By establishing these two dimensions we can choose the height and the profile based on what volume we want the mug to be. For the Monday mug we decided to go with a 3 finger handle that sat right below the lip and high enough from the table so you can fit your pinky below it. We made the width of the handle to fit the pad of your finger where it bends so it fits snug in there. The handle also is far enough away from the mug that you can have 3 fingers in there without burning them. You can also slide your hand in and cup the mug if that is your grip preference. We made the lip oval so that when you drink you don't hit your nose. We considered the production process as well and decided to make the profile of the mug to flare towards the top so we could just make a single mold for it. The last embellishment we made is to add facets. This is an easy thing to implement into the design when you model in a 3D modeling program.
Make a series of models
We began by printing a number of mug sizes to make sure the proportions were right before we made the final model that would be scaled up 13% to account for the shrinkage of our porcelain. The handle models were extremely difficult to model and print because they are really thin and complex forms. Getting a comfortable handle took dozens of 3D prints. Once we had a model in hand that felt good and was the right size we scaled it up by 13% and printed the final model that we would make the mold from. We printed the model in ABS so we could put the model in an acetone bath to remove the 3D printing texture and keep the surface clean. To finish off the model and make it easier to pull a mold off of we filled it with plaster to create a solid model.
Make a Mold
Since we designed the body of the mug to the “draftable” the mold that had to be made was fairly straight forward. A draftable model is one that can be encased in plaster without getting stuck. If the form is not draftable a multiple part mold must be made to encase the model. This was the case with the handle. Since the handle has a “top” and a “ bottom” with an apparent transition along the side we had to make two parts in order to get the handle model out of the mold. We chose to put the seamline around the spine of the handle so we could cast the model without having to clay up. After printing the handle in two parts we glue one part on the table and attach the “sprews” where we can fill the mold with liquid porcelain. The sprews have to be big enough so that when we are casting the slip fills in as it sinks in. Once the first part of the handle mold is cast we flip it over and drill “keys” into the mold. The keys act as a locking mechanism so the mold stays together tight when we strap it together and fill it with liquid porcelain slip. After drilling the keys we glue the other half of the handle to the one encased in the first part of the mold. Before pouring the second part of the mold we have to apply a mold release agent so the plaster parts dont stick together. We use murphies oil soap or vaseline. To use the soap we apply three soapy layers wiping it off between each application. You know the plaster is sealed when it gets a sheen and starts to repel water. Once the second part is poured the two parts should come apart using a rubber mallet and compressed air. This can be a tedious part of the process getting the mold parts apart but you want them to be tight! Once the parts are apart we clean all the edges so they dont chip and leave plaster chips in the slip. To prepare the molds for casting we use vinegar to removed the murphies oil soap and wash the molds thuroughly. The last step is to dry the molds. The molds must be completely dry in order to gain the most strength and be ready to fill with porcelain. We use our dry box which is equiped with a dehumidifyer and two fans to move the dry warm air around. The molds take about a day to dry in our hot box.
This is the exciting part! See our video on mixing slip in order to learn how we make our porcelain from scratch. We store our liquid porcelain slip in mixing tanks that run over night to keep the porcelain well mixed. Before casting we make sure not to mix so we dont add air bubbles to the slip. We use a double diaphragm air pump to carry the slip through tubes and into the molds. The mold must be filled over the top of the lip and into the resevoir. As the slip sets up the moistrure from the slip is absorbed into the dry plaster mold. This causes a shell to form along the mold cavity walls. The longer the slip is in the mold the thicker the shell gets. The slip that is in the middle of the mold not touching plaster stays liquid. We fill our monday mug mold for 20-25 minutes depending on a number of factors such as slip viscosity, dampness of the molds, and studio atmosphere. Once the wall is thick enough we dump the excess liquid porcelain from the interior of the mold out and let it drain upside down at an angle so it doesnt form drips on the bottom. The mug shell is left in the mold until it dries and begins to shrink away from the plaster mold cavity walls. Once the mug has dried for 30 min-1 hour the mold is ready to be opened and the new mug taken out. Before we take it out we cut the excess porcelain from the collar so we get a clean even lip every time.
The handle is cast solid. By using an old ketchup bottle we fill the interior of the handle mold and let it set up for an hour. Once it is dry the two mold parts come apart.
Clean Seams attach handle
When the mug and handle come out of the mold there are remnants from the mold process called seams. The seams are from the area where the two mold parts come together. Therefore the tighter the mold the smaller the seams. We use a series of tools to clean the seams so they arent noticeable. First we use an exacto blade to “fettle” the seam down. Once the seam is knocked down we use a fine serrated rib to smooth out the seam so it is flush with the rest of the surface. We then use a fine white sponge from Mudd tools to smooth the texture from the serrated rib. We give a quick wipe to the mug and handle to remove any blemishes that may have appeared from the first steps of the process.
Once the handle is soft leather hard we cut off the excess parts of the handle from the mold reservoirs and slip and score the attachments and apply it to the mug. Scratching the attachment and adding liquid porcelain allow the attachment to fit together like velcro. We use a soft brush and little water to wipe away any excess slip that oozes out. After this we let the mug dry to bone dry before putting it into a bisque and firing it to cone 07 or 1850F. This is the temperature our cone 6 porcelain needs to be fired to be left with the proper porosity to accept glaze. The bisque firing allows the mug to be strong and not break down when it absorbs water much like an earthenware flower pot. One test you can see for porosity is by licking the mug and seeing if your tongue sticks then you know it will absorb the moisture of the glaze.
Glaze and Surface
The glaze we use is a soft satin matte glaze that we formulated to be clean and soft. Glaze is essentially a powdered glass that gets mixed with water and then applied to a bisqued ceramic surface that melts when heated up in the kiln. We mix each color of this glaze in a separate 5 gallon bucket from scratch. See our video on glaze mixing to learn more about our process. Before glazing we wipe off any excess dust from the studio as well as spraying them down with a compressed air gun. If you dont clean the bisqued mug off enough it wont absorb the glaze and you will see a glaze flaw called crawling. Everyone glazes their mugs different ways. We use tongs to hold the mug and dunk it in and out of the bucket of glaze. The timing of how long you leave the mug in the glaze matters. The longer you hold it under the thicker the glaze builds up because the mug has more time to absorb the glaze. We formulated our glaze to be a consistency that we only have to dip in and our. To prevent drips from forming when the glaze is dumped out we use a subtle twist of our wrists to empty the glaze evenly. Once the glaze dries which takes a few minute we use a green scrubby to remove any drips or marks from the tongs. We formulated the glaze to melt enough where most of these marks are hidden but sometimes there are little clues showing how we glazed the mug. We wipe the feet so there is no glaze on the bottom so it wont melt and stick to the shelf in the kiln. Once the mug is dry we load it into a kiln and fire it to cone 6 or 2130F.
Sand and Pack
After the kiln is cool it can be unloaded. To finish the pots we want each part of them to be as smooth as possible. We use a flap sander that Forrest Lesch Middleton turned us onto to get the bottoms smooth. Once the bottoms are smooth we give the mugs a good wipe to clean them to be shipped out. We pack our mugs in geami packing material and place it in a box that fits snug. We double box everything and fill the void with kraft paper. Then its ready to go!