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Enamel cracking troubleshooting


#1

Enamel cracking sterling silver signet ring cool down

Hello!

I am hoping that some will be able to help me work through an
enameling project I am working on.

A friend offered to walk me thru the enameling, and I did not read
up on the subject extensively as I should have.

As a result, I neglected to do many things that I have since read
that I should have done.

At this stage of the process, I am trying to research and
understand:

  • why cracks in the enamel appeared after the 3rd firing (the cracks
    followed the outline of the bezel like 1.5mm thick frame around the
    edge)

(they would "heal, and then appear in another spot after each
successive firing.)

  • how the metal and enamel should be allowed to come down in temp/
    cool down.

The backstory:

  • It is basically a sterling silver signet ring, cast in Stuller
    standard silver (silver/ copper)

  • the “base” under the enameled area is approx. 5.0mm thick (did not
    hollow out. kind of (too) heavy. weighs about 28grams.)

  • It has a 1.0mm recess at the top of the ring, for an enamel
    background around a raised element

  • I did not counter enamel under the head.

  • I depletion guilded it 8 times, (pickled in Rio Pickle, burnished
    softly with steel brush and water after each firing, and neutralized
    in baking soda) (I think I was supposed to glass brush between
    firings?)

  • I used Thompson unleaded opaque enamel #1685 cobalt blue, and
    wet-packed/ fired it 4 times (I think I was supposed to glass brush
    between firings. we touched the crack on the surface.), with a 5th
    time for flash fire

  • I used diamond sanding pads to level surface before final flash
    fire (400grit and 800 grit)

I have been researching, and picked up the following

  • do not overfire past the 1400-1450.the solidus of the sterling is

(we fired at 1500 degrees F)

  • only use 1-2 layers over sterling silver, or the enamel will crack
    (mine had 4 layers)

  • the recess should have only been about.30mm deep (mine was 1.0mm
    deep)

  • the walls of the recess should be vertical and not rounded, where
    bottom meets sides, and where sides meet top (mine was rounded)

I also learned that I neglected the below as well:

  • I did not glass brush between pickling when doing depletion
    guilding

  • I did not fully dry the enamel before firings

  • I did not glass brush between firings

I am wondering:

  • if the above findings are all correct

  • and. after firing, what is the proper way to handle the piece, in
    terms of how the metal and enamel are allowed to cool down.

(I have re-read my enameling books and I cannot really find anything
about cool down technique (for heavy items like a signet ring),
except stay away from drafts, and don’t place piece on a steel block
after.

Any advice would be greatly appreciated!

I am planning to use diamond sanding pads (or my lapidary wet lap)
to grind down the height of the top down about.40mm, so that the new
depth of the recess would be approximately.40mm thick, and then
either flash fire to gloss it, or try using fine abrasives to get a
sort of shine finish. your thoughts?

Best Regards,
Julie


#2

I hope someone has some advice, as I have also had some cracking,
often days after the final firing.


#3

Hi Julie

I understand your frustration, enamel can be infuriating ! There are
several points which would cause the enamel to crack.

First - it’s a casting. If there’s any porosity in the casting, the
enamel can ping off, sometimes after several firings. Castings
should be done under inert gas avoid this. There was a discussion a
week or so ago about this, and zinc in gold alloys. Sometimes heating
& cooling several times can lessen the problem - as your depletion
process which would bring the fine silver to the surface and help
drive off some inner air bubbles. But - this is probably one of the
main reasons for your trouble.

2: the recess is too deep - take the recess and surrounding bezel
down to 0.4mm max (as you say). As long as you have no undercuts to
trap steam or air, a slighly rounded recess will affect colour depth
not adherence. If you want a clean finished edge the top bit is
better vertical.

You shouldn’t need counter enamel on a piece of this heftiness, with
5mm metal under the enamel.

3: GET RID of the glass brush!!! They are horrid tools, leave
fibreglass in your sink wastepipe, and all too often in your fingers.
Get a new natural bristle nailbrush (yes, as for your gardening
hands), mark it “enamel only” and use that instead. Brush out under
running water and rinse lots.

4: number of coats - six thin coats are better than two thick coats.
Also make sure your enamel is ground very fine and rinsed well.

You should let it dry almost completely before firing, rest it on
top of the kiln. With a very thin coat this is a bit less important.
If you don’t touch it with your fingers between coats & when
repacking, you don’t need to brush out.

5: firing temp - as long as the kiln is over 750C (sorry I don’t do
Farenheit temps) and under 1000C you’re in the right area. The
temperature that the piece reaches is more important than the kiln
temp. That sounds strange, but when the metal reaches the firing temp
of the enamel that’s when the enaml will fuse - so in a hot kiln this
will be very quick, and in a lower kiln takes longer. Open the kiln
door briefly, watch the enamel, shut the door gently if not fused
(USE GOGGLES - preferably ones to protect against infra red, but
always use goggles. Always). For the first few coats, underfire
slightly, this will help it build up thickness.

6: cooling - put the piece, in the mesh or firing support, on top of
the kiln to cool. With a thicker piece leave for longer before
moving - two minutes or more. Time for a cup of tea perhaps.

7: finishing - a flash fire is preferred, even if you matt it after,
as this seals the top surface. If you and the piece have really had
enough firings though, you can get a fairly good finish with 400 then
800 diamond pads (or adhesive diamond abrasive strip glued to a flat
thing) and then you can use ordinary jewellery wet and dry 1200 grit
paper - in a paper mandrel and pendant drill (Foredom equivalent) or
if you have the patience of Job, on a sanding stick by hand.

I do hope this helps. Sometimes a piece just refuses to get
finished, but you can take joy from the learning curve (after you’ve
finished swearing!) Good luck Tamizan, Bristol UK


#4

Hello again,

I re-read my post and wanted to clarify:

  • the cracks are not at the edge where the enamel meets the metal
    border/ frame/bezel (ie: enamel is not pulling away from the metal).

  • the cracks are sort of inset from the bezel by about 2-3 mm. They
    sort of follow the overall shape of the bezel (which is a shield
    shape), in that they are not just a straight line crack, but rather
    start and stop, following the overall curve of the shield shaped
    border.

  • cracks are sort of randomly arrayed around

  • one set of cracks will heal in firing, only to have a different
    set appear in a new location. sometimes long after the item has
    cooled.

Would also like to understand how to cool the item. I just read that
for large objects, to allow it to anneal, or cool slowly, by placing
it in another unheated kiln, or slightly heated kiln, away from
drafts. I am thinking of building a little “hut” out of new fire
bricks to let it come down in temp slowly inside it.

Hope that makes more sense!
Best Regards,
Julie


#5

When enamel cracks after a third firing, especially when it occurs
hours or days later it’s usually a sign that the enamel is too
thick. 1mm is a too thick!

When you enamel on plates of metal the counter enamel and the curve
or dome on the sheet allows the expansion/contraction of the
hot/cold enamel to flex the plate to an extent but in a ring or on a
carved surface this doesn’t happen.

I’d suggest that it’s the metal expanding and contracting that is
the most likely cause of the enamel cracking. Its contraction on
cooling is moving the metal away from the enamel edges.

If it’s possible you may consider filing down the top of the recess
or, if it’s possible, filling the recess with hard solder. This will
compromise the color of transparent enamel but probably work with
opaque.

Try using the softest (lowest fuse temperature) enamel. Grind it
yourself and wash it well using distilled water. You can also try
washing it with hydrochloric acid to remove any free iron that has
gotten into the enamel and then rinse well…

On the other hand you may be trying to use the wrong material for
the design. Consider using niello. I made my own huge batch of
niello some 20 years ago and I’m still using it but I don’t know
anyone who’s selling the stuff.


#6

An easy and inexpensive way to keep a piece from cooling too quickly
is to cover it in an inch thick ceramic fiber blanket. They can be
purchased from glass fusion/glass bead-making suppliers.

Marla
marlaandersondesigns.com


#7

There used to be a vendor in the UK who sold it a few years ago, but
I can’t seem to find them again. I think most of us just make it.
and itis great fun to make :slight_smile: Just make sure you have a good fume
hood or a breeze to your back because a nose hit of the fumes will
make you wish youhad :slight_smile: Oppi has formulas in his book. It is easy to
make, just kinda messy. Dedicate a crucible to it just like you
would any other alloy. Last time I made it. I made it on a truck
tail gate with a fan blowingacross it. sometimes you just have to
improvise.


#8

Hello,

. and I am just now reading that due to high COE of sterling
silver, I should avoid enamels with COE below 290. 
.and the opaque color I used (Thompson cobalt #1685) has a COE
of 284. 

Soooo. there is that to be added to my "should not have done"
list…!

If I am reading the Thompson Enameling Workbook correctly, page 11,
then I may try some low temp/ high expansion enamels. ?

(3000-4000 series Thompson enamels)

COE- 382-450

Firing at 1050F

Has anyone had any experience with these on Sterling silver? I would
love to hear about it.

(I really jumped into that signet ring enameling project backwards,
didn’t I ?!)

Best Regards,
Julie


#9

Hello Tony,

Thank you for your advice! All your points well noted!

I am so jealous that you are working with niello!

I have been so fascinated by it ever since reading about the process
in the Oppi Untracht book, and seeing the amazing pieces done by
Tiffany’s for the 1900 Paris Expo of the silver/ copper/ niello/
enameled/ chased/ repousse’d/ inlayed/ vessels that were Native
American inspired! To me, they seemed so very modern, compared to the
current style of the times.

Book- Pauling Farnham- Tffany’s lost genius, by John Loring (pages
60-67)

(one of my all time favorites!)

(not such which one of my Tiffany books I read this in.) but, it was
interesting to read about Tiffany’s and how their mission statement
was to produce luxury product that was accessable to the main
population, and they succeeded and continue to this day. they were
also the forerunners of having famous people/ artists design lines
under the house banner, such as Paloma Picasso, etc. interesting!

Best Regards,
Julie


#10

Hello Tam,

Thank you so much for taking the time to help me with my enameling,
I really appreciate it!

All your points are well noted! I have also re-read my two enameling
books, “The Art of Enameling” and “Enamels, Enameling, Enamelists”,
as well as my newly purchased Thompsons Enameling Workbook, and have
taken copious notes to study before attempting to fix my signet ring,
and then move on to my cufflinks project, which is similar in overall
nature, but two pieces!

I am working out how to jig the signet and cufflinks in the kiln.
the first attempt with the signet ring was less than satisfactory.

Am I correct in thinking that refractory type objects (like ceramic
kiln posts) will be ok to use, and not be as heavy of a heat sink as
stainless steel?

I am thinking of creating something along the lines of parallel bars
suspended thru a mesh bead stand for example, where I suspend the
signet, or cufflinks, between the bars

Or! Using two kiln posts and letting the ring shank cuff back hang
between them, kind of like the way a ring sits in a ring box, in a
slit, between two cushioned sides)

Just thinking. any thoughts or ideas for a jig would be greatly
appreciated!

Best Regards,
Julie


#11

Hi Julie

I use mesh supports for most things, or small steel trivets - three
points standing on a steel base.

You can use ceramic fibreboard as supports on top of a mesh, and you
can carve, stack & adapt for use. The dust is nasty.

They also smell & smoke a bit on first firing (the last lot I had
years back - may have changed).

If you are soldering before putting on enamel, there may be some
firescale on the surface to be enamelled.

Generally I enamel on clean unheated silver and solder on findings
after.

My work is mainly photoetched silver, engraved, flat sheet elements,
or good professional castings (Niagara Falls Castings UK - no
connection beyond very satisfied customer)

Once enamelled, stoned & flash fired, I pickle the pieces - dilute
sulphuric acid, or safety pickle - safety affect soft colours
sometimes, especially red and mid blues, where it causes a thin white
bloom on surface, but you can get this off when polishing.

Then I wash with soft brush & washing up liquid, rinse, and dry with
a clean soft cotton cloth. NOT touching the enamel surface, the piece
is balanced upside down on a 3 point trivet and then I solder on the
findings. This needs a steady hand (I practice “cold” after setting
up) but it’s not much harder than normal soldering.

Hope the cufflinks go well
Tamizan


#12

Julie, there is a dedicated enameling site called "Grains of Glass"
that you can google and find a large international community of
enamelists to connect with as well as those of us who come to
Orchid.

Marcie Rae


#13

Hello Tam,

Ok, great! Thanks for being so generous with your knowledge, I
really appreciate it!

I think I am going to take two small square kiln shelf “feet” and
drop the signet ring or cufflink down in between the two, and then
brace those feet with a few more “feet” stacked on each side. on a
mesh screen.

I was using the mechanics of how a ring fits in a ring box to
inspire my jig conception!

Originally I was thinking of two stainless steel tubes, parallel,
that I could drop the signet ring/ cufflink down in between.

For a holder, I was thinking of using one of those bent mesh
screens, (used for firing glass beads) and just poking the tubing
thru the mesh holes at the appropriate distance apart.

I figured originally that the round profile of a tube/ rod would be
the right shape for the ring to “sit” on, versus the squared 90
degree edge of the kiln “fee”.

But then, I got to thinking that perhaps the refractory kiln feet
would be less of a heat sink. Is that a true thought?

Anyway, I finally received my diamond grinding and polishing sponges,
pads, and plastic handled files from
http://www.ganoksin.com/gnkurl/ep820b , and so will attempt to fix
the signet tomorrow!

Best Regards,
Julie


#14

Tamizan- How do you solder on findings after enameling without
damaging the enamel?

Jo Haemer
timothywgreen.com


#15

Hi Julie

perhaps you’re overthinking the propping up a bit? If the ring will
sit flat on a mesh without the enamel touching the mesh, then that
will do just as well.

If you’re worried about the enamel falling out when dry, then mix a
drop of Klyr-fire glue in the washed and ground enamel.

Apply enamel, remove most of the water as usual, let dry. Gently
place on the mesh & fire.

Good luck and best wishes
Tamizan


#16
How do you solder on findings after enameling without damaging the
enamel? 

Carefully! But much the same as normal soldering of small things to
big things.

Basically the enamel will refire, so everywhere around needs to be
clean and dust free.

You can use soft solder, although the enamel may not refire
completely and some slight crazing can occur - I usually use hard
solder.

(Long-winded post, but read on for more detail)

I have some small steel trivets, 3 points, on which most things will
balance.

Most of my elements are fairly flat - domed but not very 3D, and
have a silver edge so I can hold without touching the enamel surface
with fingers, to avoid grease So, the enamel surface is cleaned and
dried, I apply borax & small pallions of solder to the back where
needed, and balance piece on trivet.

I have everything ready and all the findings (boraxed) in tweezers
ready to go.

I practice placing them when all is cold, to make sure that the
piece will not tip or fall, and that my hand position is steady. I
often use my little finger as a prop to keep steady! Turn on the
torch, heat the piece gently at first, then concentrate on the
solder area. The small finding is held in the shadow / bounced
flame, so it heats up but not to melting point.

The solder will ball and then flow, I place the finding at the ball
stage, torch it for a second, and then remove flame.

At this point I keep the finding in place with the tweezers until
the solder goes dull / cools a bit. Gently remove the tweezers and
hey presto.

For two or more findings, the same process. move the flame away,
wait until the first solder is secure, pick up next tweezers and
repeat.

Air cool. When cold, I give the findings a jolly good tug
(destruction testing!) and refire if loose or poor joint.

Just like normal soldering, only balanced on a trivet.

Don’t let the flame bounce off the trivet onto the enamel surface,
or it may burn or discolour, like raku glaze.


#17

So I’m guessing that your pieces are not counter enameled? -Jo


#18

Enameling is the most sensitive art master. Either the enamel is too
thick. Or the metal is too thin or too thick. It’s always a
challenge. Kim


#19
So I'm guessing that your pieces are not counter enameled? 

Jo - not counter enamelled. I use 1.3 to 1.5mm thick sterling with a
0.3mm recess, which is then engraved to a further 0.15mm depth.

So, the depth of enamel is 0.45mm max on a 0.85 min thickness. This
will not warp so no need to counter.

Best wishes from sunny Bristol, SW England


#20

Hello Marla,

Thanks for the suggestion about a furnace blanket!! I am going to
order some!

Best Regards,
Julie