How to Rehydrate or Reconstitute Dry Metal Clay
Rehydrate Dry Metal Clay Scraps, Filing Dust, Broken Greenware, or Entire Packages of Dried Metal Clay Back Into Fresh, Pliable Clay!
Pretty much any form of dried metal clay that hasn't been fired—with the exception of overlay paste or oil paste—can be reconstituted to a nice, pliable working consistency again. It's just a matter of rehydrating the clay to replenish the evaporated water and giving the rehydrated clay enough time for the binder to absorb the moisture completely and be reactivated. (Tom Petty was right, the waiting is the hardest part!)
You can reclaim your dried scraps and bits of metal clay, filing or sanding dust, greenware that breaks and can't be repaired, or unfired pieces that you decide you don't like or want to re-make from scratch.
With the skyrocketing price of metals and, therefore, metal clay, it makes sense to reclaim every bit of usable material! Why turn your metal clay scraps and filing dust into slip when you can turn it back into clay? (You can always thin a little of the clay with water as needed when you need a little slip or paste.)
There are several different approaches for reconstituting dried metal clay. Which one you choose in a given situation depends on how quickly you need to use the reconstituted clay and how much energy you want to put into bringing it back to a workable consistency.
Chopping, Crushing or Grinding Dried Metal Clay
Keep Dedicated Tools for This Purpose
Most of the methods for reconstituting dried metal clay involve chopping, crushing or grinding the clay before rehydrating it. There are various tools to help you accomplish this. Regardless of which tools you choose, make sure to use them only with metal clay!
Also, I strongly recommend using a particulate respirator rated for dust (or at the very least a dust mask) to protect your lungs from breathing the metal clay dust as it's stirred up into the air. Yes, it's a nuisance, but protecting your health is important!
It's important to choose the right particulate respirator. You want one that is NIOSH rated N95 or N100. Also, choosing a particulate respirator that is cool and comfortable to wear will greatly increase the chances of your wearing it—and it can't protect your lungs unless you do!
Choose the Right Particulate Respirator or Dust Mask
While the N95-rated 3M 8511 is a widely used model, the newer 3M 9211 Cool-Flow N95 Particulate Sanding Respirator has some important advantages. It's lighter weight, cooler and more comfortable to wear, especially in hot or humid conditions. The 9211 is made of a softer, pliable material while the 8511 is molded, so not only is it more comfortable it also fits a wider range of face sizes and shapes. In the same vein, the chin section of the mask opens up to cover your entire chin, including the underside, whereas the 8511 and other molded masks just sit in front of your chin. The patented 3M cool flow exhalation keeps you cooler and more dry than the molded masks that can cause your face to perspire. Last, you can order an economical that come folded flat and individually sealed to keep them clean until you're ready to use them. 10-pack of 3M 9211 particulate respirators
Chopping, Crushing and Grinding Equipment
Option 1: Electric Coffee Grinder or Spice Grinder
My favorite tool for pulverizing dried metal clay is an electric coffee grinder or spice grinder, the kind that grinds the contents inside an enclosed compartment. It's fast, efficient, and it prevents the fine metal clay dust from becoming airborne as it's being ground so you're less likely to breathe it into your lungs.
Sometimes you can find these grinders at yard sales or thrift stores, but since metal clay is going to be harder on the motor and blades than coffee beans or spices I usually buy mine new. They don't cost that much and I haven't had to replace either of mine yet. (I have one for silver clay formulas and another for base metal formulas.) The is a very good model for this purpose. Krups F203 Electric Spice and Coffee Grinder with stainless steel blades
Tip: Shaking the grinder up and down like a cocktail shaker while it's running will help move all the little bits of clay into the blades.
After you turn off the grinder, tap it smartly on your work surface to get most of the clay dust to settle into the bottom of the compartment.
Option 2: Mortar and Pestle
I much prefer using an electric coffee grinder, which creates a very fine powder that's easy to rehydrate and is much easier on my hands. I find that using a mortar and pestle can be a bit hard on the palm of the hand that's holding the pestle (i.e., the grinding stick). So if you have limited hand strength, arthritis, bursitis, etc., you're better off using a dedicated coffee grinder. However, using a mortar and pestle is fine if you only need to grind a small amount of dried clay at a time, or if it doesn't hurt your palm the way it does mine.
If you use this method I recommend tenting the mortar and pestle with plastic wrap as you work to keep the metal clay dust as contained as possible. And, of course, be sure to wear a particulate respirator or at the very least a dust mask to help prevent yourself from breathing the airborne metal particles.
Option 3: Rigid Clay Blade
If your pieces of dried clay are large, you can use a rigid stainless steel clay blade to chop them into small bits.
These pieces can be reconstituted as is, and many artists do just that. However in my experience these chopped up bits sometimes can produce in lumpy reconstituted clay, especially if you aren't patient enough to let all the water absorb fully into the binder.
To avoid lumpy clay I recommend that you grind the chopped clay bits with a mortar and pestle (chopping the clay first makes the grinding much easier!), place them inside a heavy plastic bag, such as a freezer bag and crush the bits into a powder with a heavy rolling pin (or a similar substitute, such as an unopened bottle of wine), or dump them into a coffee grinder dedicated to metal clay use and pulverize them for the smoothest reconstituted clay.
Removing Debris Before Reconstituting Your Clay
Metal clay sanding dust may contain tiny amounts of abrasive grit from sanding pads, sponges or sticks, sandpaper or salon boards (especially very inexpensive, inferior quality sandpaper or salon boards). If you have a pet that sheds, you might end up with a few pet hairs or other debris that needs to be removed. And there are other types of debris that can end up in your metal clay dust or scraps.
If you suspect that there may be any type of grit , pet hair, or other debris in the dried clay or dust you want to reconstitute, it's a good idea to grind all the clay you are reconstituting into a fine powder and then strain or sift it through a piece of stainless steel mesh (such as an 80-mesh enamel sifter) or coarsely-woven nylon material before rehydrating it.
To protect yourself from breathing in metal clay dust, I recommend the following precautions:
- Wear a dust mask at a minimum, or preferably a particulate respirator.
- Grind your clay in an electric coffee or spice grinder to keep the clay dust from dispersing into the air.
- After the clay has been ground into a powder, tap the grinder on a table or counter top and let the dust settle before opening it.
- Consider placing your hands, the clay dust, the sifting screen, and the collection container inside a large, gallon-size plastic bag (or tenting your hands and what you're working with a large sheet of plastic wrap) while sifting the clay to help minimize the dispersion of the dust into the air.
- If you will not be reconstituting the clay immediately, cover the container tightly until you're ready to reconstitute the clay dust.
Patience Is the Key to Reconstituting Metal Clay Successfully!
It's important to add back the moisture gradually, a little at a time, and/or allow enough time for the clay to absorb the moisture fully.
It's easy to add more water, if needed, and just set it aside to be absorbed. But if you add too much and the clay can't absorb it all, you'll have a slippery mess that will need to dry out. And you'll need to monitor and knead it frequently to keep the moisture evenly distributed throughout it and make sure the clay doesn't dry out too much.
My Favorite Way to Reconstitute Dried Metal Clay
The following method takes a bit longer than the others I'll describe, but I find that it produces a perfect working consistency reliably.
- Start by grinding your clay into a fine powder, using any of the methods described in the section on Chopping, Crushing or Grinding Dried Metal Clay.
- Strain or sift the clay dust into a small bowl or onto a piece of clean glass (see the section on Removing Debris Before Reconstituting Your Clay).
Note: While this step is optional, it's a good idea even if there isn't any debris in your clay, because it will separate out any bits of dried clay that weren't pulverized, and it also aerates the clay dust a bit so that it's easier for the moisture to reach the binder.
- Still wearing the particulate respirator or dust mask you put on while grinding and sifting the clay, hold a mister bottle filled with water about 8" to 12" above the metal clay dust, aim it at the clay, and pump just one or two light spritzes of water (no more than that!), so that the mist of water settles down gently onto the clay dust. (This prevents the pressure from the spray from blowing the dust around.)
Tip: You can use a pipette to add a drop or two of water instead of misting it, but a mister will distribute the water throughout the dust much more evenly.
- Using a small stainless steel spatula (I find that plastic spatulas break too easily when used for this purpose), gently mix the water into the clay, using a folding motion (as you would to mix flour or beaten egg whites into a cake batter).
Important: Fold the moisture into the clay dust slowly and gently to avoid dispersing the clay dust into the air any more than necessary.
- Mash the moisture into the clay powder with the spatula to help the binder absorb it as much as possible.
- Spray on another light mist of water from time to time (always from a height, as before), stirring and mashing the moisture into the clay dust as much as possible before adding more water.
Important: The key is to be patient and take your time, adding only small amounts of water stirring and mashing in each new addition before adding more water! This will make it easier for the binder to absorb the water evenly, and will help reactivate the binder. Adding too much water at a time also will create slip, making it harder to get all of it out of the bowl or off the glass and back into the mass of clay.
- Continue the misting, stirring and mashing cycle until the clay starts to pull together in little clumps.
- Add only one or possibly two more spritzes of water and then just keep mashing in the moisture patiently.
- As soon as the clumps start to pull together into a more cohesive mass, stop adding water! The clay still will look too dry at this point, but it's okay.
- Scrape the clay onto a piece of Freeze-tite (a heavy plastic wrap designed to protect food from freezer burn), or inside a gallon-sized, thick plastic food storage bag intended for freezing food, or onto two stacked sheets of regular plastic wrap, the heaviest thickness you can find.
Tip: Don't use Glad Press'n Seal because the clay will stick to the adhesive side of the plastic wrap.
- Either knead the clay very thoroughly inside the plastic bag or wrap, or, better yet, roll it out as thinly as possible inside the plastic, which will force the water into the binder evenly throughout the clay. Thanks to Lisa Cain of the Mid Cornwall School of Jewellery for this fantastic tip.
- Fold or roll the clay and press it firmly into a compact patty ball inside the plastic.
Another great tip from Lisa: If the clay still seems too dry, roll it out again inside the plastic as thinly as possible (to maximize the surface area) and spritz it lightly with water. Fold the clay over to trap the water inside, and then re-roll it inside the plastic to press the moisture into the binder.
- Wrap the rehydrated clay tightly in plastic and let it rest for least 30 minutes (and preferably overnight).
- Knead the clay again briefly through the plastic just before using it. Be sure to watch Lisa's wonderful video demonstration of this method below!
Lisa Cain's Fantastic Video Demo / Tutorial
Lisa Cain, who runs the highly respected Mid Cornwall School of Jewellery and is the executive director of the UK PMC Guild, has published a fantastic video tutorial that demonstrates my favorite method for reconstituting metal clay. This video is a must-watch!
Mary Ellin D'Agostino's Tips on Improving Clay Consistency
PMC Connection's Technical Advisor Mary Ellin D'Agostino discusses her approach to reconstituting dried metal clay in her excellent post on improving clay consistency in PMCC's CornerStone blog.
The Mortar, Pestle and Glycerin Method
Artist Angela Baduel-Crispin pulverizes the dried clay in a mortar and pestle. She adds small amounts of water at a time, mixing and mashing it in with a spatula, and recommends adding a bit of glycerin to help make the clay pliable, although it's optional. Here's a link to Angela Crispin's Reconstituting Dried Metal Clay photo tutorial on Flickr in which she explains the steps clearly and succinctly.
If You're Willing To Spend More Time Than Effort
If you have a lump of dried clay and you're not in a hurry to reconstitute it, there's no need to spend time grinding, grating or chopping it into small pieces. Just put the dried clay it into a sealed container or zippered plastic sandwich bag with some water and set it aside for a day or two (or three, depending on the size and amount of clay you're reconstituting). From time to time, stir, mash, or knead in the water to the best of your ability, and then seal up the mixture and set it aside again. Repeat this cycle until all the water is absorbed into the clay. If the reconstituted clay is too dry, knead in a little more water and set it aside to rest, preferably overnight.
To make it a bit easier for the water to penetrate and be absorbed, you can drill a few holes into the lump of dried clay, if you want to. But if you're willing to be patient, it isn't necessary.
Additives for Improving the Consistency of Reconstituted Metal Clay
There are several factors that can affect the consistency of reconstituted clay adversely:
- If the dry clay is very old, the binder may have degraded somewhat.
- The clay may have been contaminated with too much olive oil, Badger® Balm, or other clay release agent.
- If you used a cream, balm or lotion containing petroleum or petroleum derivatives (petroleum jelly, for example) on your hands, tools, or textures, it will contaminate the clay (and will not burn out cleanly in the kiln).
- If you apply a skin shielding lotion (such as Gloves in a Bottle™) to your hands but don't let it dry before touching the clay, it can contaminate the clay.
If your reconstituted clay doesn't have the same consistency as clay straight from the package, you can mix in one of the following additives, which may improve the clay's consistency:
- I and many other metal clay artists routinely add some new, fresh clay straight from the package to each batch of reconstituted clay (generally a 50/50 mix of fresh to reconstituted clay). This adds some fresh binder and also dilutes the proportion of any contaminants in the clay.
- Kneading in a few drops of lavender oil can improve the clay's workability.
- Another option is to mix in a very small amount of glycerin, preferably diluted with water (1 part glycerin to 3 parts water).
- Note: If you add too much glycerin, the clay will remain flexible even after it dries, which will make it difficult to sand or file cleanly. The clay also may become crumbly.
- Some artists add in a small amount of CMC (carboxymethyl cellulose, also known as cellulose gum), which is a plant-based starch used in the food industry as a thickener. Many people believe that CMC (or a similar cellulose-based starch) is one of the organic binders used in commercial metal clay formulas. Adding a little CMC to reconstituted clay can serve to replace some of the degraded binder.
- It's important to note that if you add more binder to the clay, it will shrink more based on the higher proportion of binder to metal particles.
Once you've kneaded any of these additives thoroughly into your reconstituted metal clay, set the clay aside in a storage container that will keep it moist (see my article on Metal Clay Storage) for at least 30 minutes, and preferably a day or two. This will allow the additives to be absorbed into the clay completely. Then knead the clay well before using it.