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Sterling Silver Clay - A Natural Evolution by Lisa Cain

HallmarkOn 27th January 2011 I held the first ever piece of officially Hallmarked Sterling Clay in my hands. For me this was an exciting moment and the culmination of a lot of experimentation. Actual proof that I had achieved what I set out to do.


My aim was to come up with a method, recipe and firing schedule that could be replicated in the home studio and which would work regardless of your brand preference. As an artist, it was definitely a challenge for me to put on my ‘scientific’ head but I knew I wanted strength AND hallmark quality Sterling silver in a clay form. I was convinced it could be done and, quite frankly, no one else was going to do it for me. I’m delighted to say that, with lots of help from colleagues, fellow artists, friends and family, this is now possible for everyone.


Once I knew that Sterling Clay was achievable and started to tell others, some people encouraged me to manufacture the Sterling Clay or patent the recipe but, even if it were possible, this simply doesn’t interest me.


My focus is set firmly on innovation, artistry in metal clay, teaching and running the Mid Cornwall School of Jewellery.


My motivation was the very real need for this type of clay, especially here in the UK where Hallmarking laws influence the materials we, as artists, can credibly use in our commercial work. I share it with you willingly.


Please ‘pay it forward’ and share any observations, difficulties, tips or discoveries you make when working with Sterling Clay on our purpose-built MCSJ Sterling Clay Group


There is a lot yet to be discovered about Sterling Clay so here’s how to get creating!


ToolsSterling Clay Tools


Accurate digital scales




Plastic wrap


Coconut shell charcoal & steel firing container



To make 20g of Sterling Clay

PMCPro 15g

PMC3 5g


Art Clay Silver 18.5g

Art Clay Copper 1.5g


Tips - Remove any dark patches of oxide from the Copper Clay before mixing as it may interfere with sintering.

Note - if Hallmarking is crucial to you; add a little extra fine silver clay (about 1g) to be certain that your mix will be ‘sweet’. This won’t affect the sintering.



1) Once you have weighed out both your clays make some long thin snakes.Blending the Clay


2) Split these long snakes into threes and begin blending the two types of clay with spatula.


Tip - splitting the 20g into smaller amounts makes it easier to blend each lump thoroughly.


3) When you have blended all three segments, combine into one lump, blend & extrude repeatedly. Use the extruder head with the smallest holes to aid blending.

Extruding the mixed clay











Bad mixContinue to mix, extrude and blend the clay until you have a uniform colour with no signs of streaks or blotches. The image on the left shows a bad mix.








4) Press or roll a thin sheet of the Sterling Clay and place in plastic wrap, spray with a little extra water, close up and leave to sit overnight.

5) Make something fabulous!

6) Refine as normal and dry thoroughly before firing




Step 1

Fire on kiln shelf uncovered @ 538C/1000F for 30 minutes

Place on top of 1cm base layer coconut shell carbon in steel container and cover with 1 or 2 cm coconut shell carbon. Lid on.


Step 2

Fire @ 821C/1510F for 1 hour.

Tip-Use a small steel container and small quantities of charcoal wherever possible Note-we have had success torch firing instead of Step 1.

Lesley Messam also had success simply torch firing the ACS/Copper Clay mix.



Avoid cross contamination to your fine silver clay by cleaning all tools and keep sanding tools separated.




Lisa Cain RingPost firing strength is excellent.

Solders and behaves very similar to traditional sterling. Unfortunately this includes fire stain.

Slightly more porous than traditional sterling so burnish before soldering.

Best to use medium or easy solder.

Has quite a grey appearance but polishes and burnishes nicely.

More scratch resistant than fine silver.


Overall the Sterling Clays seem to need more water and more time to absorb water in order to keep the clay workable.

So far, the PRO/3 Sterling mix has been the favourite in terms of workability, ease of mixing and longer shelf life.


The Art Clay Sterling mix tends to separate and oxidise if left unused so mix it and use it ASAP. For the same reasons, only mix Art Clay Sterling slip as you need it. One tester also found it unusually difficult to repair a broken piece at the greenware stage.


There are still quite a few unpredictable factors like bubbles appearing in the silver during sintering (rare but happens with both brands) and a range of shrinkage in ring sizes ranging from 5 to 10 sizes in one firing!



20-25% (PRO/3 mix shrinks slightly more than Art Clay mix)


To date, after extensive trials, I have not been able to find a successful firing when using Hadar's Copper powder and silver clay powder.


Big thanks go to Chris Pate, Lesley Messam and Julia Rai for testing Sterling Clay, giving up their time at short notice and sharing their results. Thanks also to my Dad for help with the algebraic equations needed for the PRO/3 mix. Maths is not my strong point!


What’s it good for?


Since it is labour intensive to make Sterling Clay, it would seem wise to use it selectively and it certainly won’t replace the silver clays we are already using. And yet it is another useful tool in your ever-expanding tool box. Use this clay where you want strength and high shrinkage or need Hallmark quality Sterling silver with the ease of working in clay.


I opted to make a few pieces which would be too fragile in fine silver clay and too time consuming or difficult to make in traditional sterling. But honestly most of my time was absorbed into getting the clay mix and firing schedule right at the ‘science’ end. Consequently I haven’t actually had much time to explore the clay artistically yet. As I write this I am smiling because I can’t wait to see what others choose to do with it!



It amazes me that fourteen years into the metal clay game I am STILL excited by this material. I have yet to reach the boundaries of what I can do with it and feel lucky to be part of such a pioneering community.


Long may it continue.