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Exploding hollow bodies


#1

G’day; I’d like to add my 2c worth to the previous comments on
soldering hollow bodies. One does of course , make a tiny hole
in an unobtrusive spot, with the smallest drill available. If
you can’t get a really small drill (1mm or less) make one from a
needle. (write me off line and I’ll show you how). However, now
comes the tricky bit; you have soldered the job and put it in
pickle to remove scale. But it is almost impossible to keep the
pickle from getting into the hole, though you could block it
temporarily with children’s modelling clay. If some pickle does
get in, the only way to remove it is to first wash it out, by
gently heating the job, immersing it in clean cold water and
repeating until no pickle remains. Then you have to dry it out.
I recommend heating it until a wisp of steam emerges from the
hole, then placing the job in an airtight jar containing silica
gel drying agent. It might take a few days, but it WILL dry out.
Of course if you could evacuate the dryer container, the drying
would take place much faster.

    /\
   / /
  / /      Johnb@ts.co.nz
 / /__|\
(_______)  In sunny Mapua NZ

#2

Hollow objects are very common in Asian jewelry designs. Indian
and Indonesian craftsmen generally leave a small hidden hole to
allow gases release. Thai on the other hand, are commonly
practicing, the rather dangerous, complete object sealing.
Sometimes even applying additional soldering cycles to the
hollow object without explosion!!

This is a very common practice in Thailand, called “PraKop”. An
experienced “Prakoper” can easily solder a couple of hundred
objects a day!

General Tips.

Solder. - Use very easy flow solder.

Clean the suture by grinding using sandpaper. #150 will do just
fine.

I prefer to use wire solder cut into jump rings for round
objects. The rings should be just smaller than the object mouth.
By placing two rings, you should have a full cover of inner side
of the suture line.

I Use point pre-soldering along the suture for other shapes.

Immerse the entire object in flux and re-position the solder
rings. Apply quick heat to dry.

Heating - Experienced use of the torch is the key for successful
soldering. Operation should be quick and even. Use tweezers to
gently press the two parts together and lead the solder with the
flame along the suture. Apply extra flux to areas that hasn’t
been sealed properly and reheat. Do not let the object to cool.
Keep heating gently while applying the extra flux. Experienced
workers usually reach complete sealing in only one heating cycle.

Cooling of the piece after soldering should be slow and
graduate. Never immerse the hot hollow in water. It is impossible
to reheat hollows that were quick-cooled.

Re-heating - Never re-heat object that had been cooled in water.
Do not pickle hollows. File it instead! Re-heating should be
graduate and done with extreme caution. It is an extremely
dangerous operation! You might considering drilling a hole to
allow gases escape.

Always wear your safety gear!!

Have a good day!

Hanuman

Dr. E. Aspler
@Dr_E_Aspler2
Managing Director
Ganoksin Jewelry Co.,Ltd

Webmaster Ganoksin Online

ICQ # 258 49350


#3

I have never heard that it is impossible to reheat hollows that
were quick- cooled. What is the reason?

Alan


#4

Hi all, the exploding hollow bodies can also relate to
spiculums… remember the recent thread on how to make them.
Please make sure that there is a hole for the air to escape. This
can be at the end of one of the points. If the “joint” section
gets soldered up, you can take a small round burr, make a little
depression and then key in a .7mm drill bit into your pendant
drill and gently drill a hole thru, ie up the length of the
spiculum. This means it is invisible. I recall soldering backs
onto a spiculum once and suddenly there was this loud “whoosH” as
the spiculum took off and slammed into a far door. I was very
lucky that the pointy end was not pointing towards me! A lesson
learned, to always check the escape hole!

Felicity in beautiful West Oz where autumn is in the air.


#5

Hi all, the exploding hollow bodies can also relate to
spiculums… remember the recent thread on how to make them.
Please make sure that there is a hole for the air to escape. This
can be at the end of one of the points. If the “joint” section
gets soldered up, you can take a small round burr, make a little
depression and then key in a .7mm drill bit into your pendant
drill and gently drill a hole thru, ie up the length of the
spiculum. This means it is invisible. I recall soldering backs
onto a spiculum once and suddenly there was this loud “whoosH” as
the spiculum took off and slammed into a far door. I was very
lucky that the pointy end was not pointing towards me! A lesson
learned, to always check the escape hole!

Felicity in beautiful West Oz where autumn is in the air.


#6

Hello Allan, I think the reason is that a tiny hole might be in
the piece. Theoretically not, but in the real world, a bit of
dirt might be present or a bit of porosity. After soldering, the
air inside cools and contracts, creating a vacume. If there is a
leak anywhere at all, even if you can’t see it, air will seep in.
Nature abhors a vacume. When you reheat the piece , air will want
to escape because it expands quickly. With no place to go
quickly, pressure will build up and an explosion can take place.


#7
I have never heard that it is impossible to reheat hollows that
were quick- cooled. What is the reason?

Hey Alan, My experience has been that if there is a leak, quick
cooling will tend to allow more moisture whether acid or water to
enter the work. Makes for quick exploding if one needs to reheat
any time soon.

Bruce D. Holmgrain
Marylands first JA certified Master Bench Jeweler
Http://www.goldwerx.com
@Bruce_Holmgrain


#8

I have never heard that it is impossible to reheat hollows that
were quick- cooled. What is the reason?

Pin hole leaks in most solder joints allow small amounts of
water /pickle into hollow and then when heated it flashes to
steam then bang! If you air cool no water no bang maybe it all
depends on how thick the shell is and how well the seam was
sealed when it was soldered. If the seam was totally sealed when
soldered then there is actually a partial vacuum in the hollow
due to the expansion of the heated air which then contracts when
the shell cools. When you heat it again it expands to about
atmosphereic pressure rather than a higher pressure. If there are
pinholes the air will expand to greater than atmospheric pressure
and then bang.

Jim


@jbin
James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601
510-436-3552