How To - Experimenting with Decals

Ceramic Decals... for the first few years I was learning about my craft/art (ceramics)...I had my head set on being a "purist".  No decals, no alternative firing or finishing techniques...everything would be stoneware and glazes.  That's it.  Well, as I've evolved as an artist and learned more...I've come to realize that there's nothing wrong with using tools of the trade, as well as alternative finishing techniques.  At least for me since my items are sculptural and very rarely do I make functional ware anymore.  It's just not my passion...sculpting is.  Where this has led...is me acquiring lots of different ceramic decals for a sculpture idea I had (as well as some limited edition ceramic ornaments!...stay tuned for those..).  But I wanted to still be able to fire my ceramics to their maturity temperature of ^6 (cone 6, which is roughly 2200*F).  But all the literature I'd read on ceramic decals said that they had to be applied on already glazed/finished ware, and fired to a much lower temperature.  So I took this as a challenge.  I searched for an additive I could add to either the greenware piece of pottery in an effort to raise the maturing temperature of the colorants used on the decals.  I discovered that silica is a product used to raise the melting temperature in certain glazes.  Luckily, I had some on hand...so experimenting I went!  These are my results of my first tests.


*HEALTH AND SAFETY NOTE*
When mixing any sort of chemicals, especially silica, it is important to wear proper safety gear, to include gloves and a respirator/mask rated for fine particulates.  This helps mitigate the risk of silicosis, among other things, that is caused by exposure to silica dust.

First thing's first.  I have small 5.5 oz plastic food containers.. like the kinds restaurants use to send home sauces when you get something to go.  These I have found work great for testing glaze or underglaze recipes.  Each test uses 50g/50ml of water as the base suspension.  I mixed 1% of the suspension (so 0.5g) of epsom salts into each one.  Epsom salts are often used to help keep a mixture in suspension and keep the different additives from settling at the bottom.  Well...I either didn't use enough epsom salt in these suspensions, or I need to add something else because the silica still settled at the bottom, but didn't harden up.  So that's ok. 

PROCESS
 Prelude - Each test tile/disc has all the same decals, but a different solution used to separate the decal from it's paper backing.  These are the percentages:

• Tile 1 - 50ml water, 1% epsom salt (0.5g), 1% silica (0.5g)
• Tile 2 - 50ml water, 1% epsom salt (0.5g), 2% silica (1.0g)
• Tile 3 - 50ml water, 1% epsom salt (0.5g), 3% silica (1.5g)
• Tile 4 - 50ml water, 1% epsom salt (0.5g), 4% silica (2.0g)
• Tile 5 - 50ml water, 1% epsom salt (0.5g), 5% silica (2.5g)

Step 1:  I cut out all the decals and premixed all the solutions (forgot to take a picture of that process though..) 

 Step 2:  Ensure the mixture/solution is thoroughly mixed (I had to mix it before placing each decal in the water).  Place a single decal (or two or three small ones) into the suspension.

Step 3:  With tweezers, slide the decal off the paper and remove the paper from the suspension.  I then put the decal BACK INTO the water.  I wanted the silica to adhere to the paints used to create the decal, hoping that this would increase the melting temperature of the colors used. (in the picture I'm using my fingers but found tweezers worked better)

Step 4:  After letting the decals soak for a few more minutes, use tweezers to pull the decal out and apply it to the test tile.  I then used a small make up brush to brush (GENTLY) any air bubbles out.  Mind you, I did this test on bone dry tiles...NO glaze...which is on my next trial run...to apply a clear glaze over bone dry and see if that makes a difference.

 

Step 5:  Load m into the kiln and cross your fingers!  haha  I took pictures and documented each tile of what they looked like before firing and after.  In tiles 4 and 5, I also did a thin brushed on layer of the water/silica solution.  Not sure if that small extra step helped some or not.

 

RESULTS

• Tile 1 - 50ml water, 1% epsom salt (0.5g), 1% silica (0.5g)

The yellows and reds are gone, completely burned out.  There is some blistering which I'm not sure is a result of no clear glaze, any small puddles of solution that got left on top of the decal before firing..  It seems to have occurred regardless of color, as it's present on blue, green, yellow, red...So Tile 1...fail.

• Tile 2 - 50ml water, 1% epsom salt (0.5g), 2% silica (1.0g)

 Basically a repeat of test tile 1.  The small blue flowers on top seemed to have faired a bit better.  We can actually SEE the outline of the cross on this one though.. so that's an improvement.  Tile 2..Fail

• Tile 3 - 50ml water, 1% epsom salt (0.5g), 3% silica (1.5g)

Looking a little better than tiles 1 and 2.  Less blistering.  The small blue flowers look awesome!  So do the blue daisies.  These 2 decals in particular seem to have faired well regardless of the silica concentration.  The green of the purple rose's leaf looks more avacado and blistered bad.  As did the iris.  However, it seems the purple in the iris did a tad better.  Still burned out to look brown... but better.   I really do love the ghost effect of the larger rose...how the purple/pink turns into the gray blue.  Still, ultimately...Fail.

 

• Tile 4 - 50ml water, 1% epsom salt (0.5g), 4% silica (2.0g)

We can actually see the rose outline for those itty bitty red roses in the lower right hand corner.  Tad more detail is visible on the cross (though still blistered badly).  I'm really beginning to think the blistering has something to do with a) the lack of clear glaze and b) puddles of the silica solution sitting on top of the decal after application.  More details in the large rose's leaf is visible, less burned out and less blistering.  Not a complete failure..but not quite what I'm looking for.

•  Tile 5 - 50ml water, 1% epsom salt (0.5g), 5% silica (2.5g)

 I think I might be onto something here.  The gold rose was still completely obliterated.  However, there's actually a hint of red on the itty bitty red roses on the bottom!  More detail than the previous tile for the cross.  More detail is visible on the hummingbird decal.  Surprisingly the blue daisies blistered and faded!  Those little buggers have faired the best throughout this experiment!

 What I  Learned

• Yellow DEFINITELY burns out at ^6 temperature, even if the outline and details become visible with the higher silica concentration solution.  
• Red, same thing, however with the higher silica concentration the details do begin to appear even if the red color disappears.  
• Blues and some shades of green hold up the best at high temperatures.  I'm going to assume that this is due to the cobalt oxide that is likely used as the colorant in these pigments.
• Blistering is a big issue.

Questions To Explore/Further Testing

• Is the blistering a result of no clear glaze topcoat under the decals?  Because the decals were applied to bone dry greenware rather than finished/bisqued pieces?  Or is it a result of small pools/puddles of silica solution on top of the decal?  Lots of troubleshooting to do on this one.
• Would the color saturation have been better or more vibrant if I had allowed the decal to sit in the solution longer? 

So needless to say...I think I answered a few questions but more were raised.
Can decals be successfully fired to ^6?  YES
Can decals be successfully single fired to ^6?  YES, depending on the color of the decal.
Can the decals be successfully fired on bone dry green ware?  YES 

Let the experimenting continue!  Don't be afraid to break the "rules" of whatever craft/art you are involved in.  That's how we learn and how new discoveries/advancements are made.