Paper clay slip is one of the most useful repair tools in a ceramics studio. Unlike standard joining slip, it bonds across moisture levels — you can apply it to bone dry clay and have the join hold through firing. It’s made the same way as regular joining slip but uses paper clay instead of standard clay, which means the fiber network carries across the join and reinforces it in a way that plain slip cannot.
How It Differs from Standard Joining Slip
Standard joining slip works by rehydrating both surfaces and allowing them to bond as they dry at the same rate. When moisture levels are mismatched — one piece wet, one bone dry — the dry piece absorbs moisture from the slip too fast, the bond forms unevenly, and the join cracks as the two pieces dry at different rates. Paper clay slip solves this because the cellulose fibers bridge the join mechanically. Even if the moisture differential is significant, the fibers hold the two surfaces together while they equalize.
Making Paper Clay Slip
The process is the same as making standard joining slip — just use paper clay instead of regular clay as your base material.
Method 1: From Dry Paper Clay Scraps
- Collect bone dry paper clay scraps and trimmings — from the same clay body you’re working with
- Break into small pieces and place in a sealed bag, crush with a rubber mallet to a rough powder
- Add to a container with water and let soak overnight
- Blend with an immersion blender until smooth
- Adjust consistency with water until it reaches thick cream — spreadable but not runny
Method 2: Thin Down Wet Paper Clay
The quickest method. Take a small amount of wet paper clay, add water gradually, and work it between your fingers until it reaches a thick slip consistency. Use immediately. This works well for on-the-spot repairs during a building session.
Liquid Choice
- Water: Works for most joins where pieces are at similar moisture levels
- Vinegar: Adds tack and mild deflocculant action — good for leather-hard to leather-hard joins
- Magic water: Strongest option — use for bone dry repairs and most critical joins
Repairing Cracks in Leather-Hard Clay
- Press the crack closed gently with your fingers if it has opened slightly
- Work paper clay slip into the crack with a stiff brush, pushing it into the full depth of the crack
- Smooth the surface with a damp finger or rubber rib
- Cover loosely with plastic and dry slowly — rapid drying after a repair is the most common cause of the repair failing
- Tip: If the crack has opened wide, roll a thin coil of wet paper clay and press it into the crack before applying slip over the top. The coil fills the gap; the slip seals the surface.
Repairing Bone Dry Pieces
Bone dry clay is fragile and standard slip won’t bond to it reliably. Paper clay slip made with magic water is the most effective approach:
- Brush a thin coat of magic water onto the bone dry surface around the crack or join area and let it absorb for 30 seconds
- Apply paper clay slip with a brush, working it firmly into the crack or onto the join surface
- If joining two dry pieces, apply slip to both surfaces and press together gently
- Support the join so it doesn’t move while drying — prop against a foam pad, use small rolled clay supports
- Dry extremely slowly — cover and leave for 24–48 hours before unwrapping
- Tip: Don’t try to smooth bone dry repairs aggressively — you’ll damage the surrounding surface. Light smoothing with a barely damp brush is enough. Final cleanup can be done with fine sandpaper after bisque.
Adding Handles to Dry Mugs
The classic paper clay repair scenario. Score the attachment points lightly with a needle tool — don’t score aggressively on bone dry clay as it chips. Brush magic water onto both surfaces, apply paper clay slip, press the handle firmly against the body, and blend the edges with a damp brush. Dry very slowly wrapped in plastic for 48 hours. The join won’t be as strong as a leather-hard attachment but will hold through firing if the drying is slow and even.
Storage
Paper clay slip keeps well in a sealed container for several weeks. Add a small amount of dish soap to inhibit mold growth. Stir before each use. If it thickens over time, add a small amount of water and mix. Label the container with the clay body so you don’t mix slip from different bodies.
Related
See also: What Is Paper Clay?, How to Make Paper Clay, and Slipping and Scoring.
