I’m doing more work with small pierced designs and wondered if
anyone out there has made thrumming threads and will share how
they’re made. I need something thin, flexible, and abrasive that
will fit in the tiny holes (1-2mm or less).
I’ve tried using very thin strips of sanding paper, but after just a
little bit of pressure from sanding they break.
I’m also a weaver in addition to being a silversmith, and my left
over warp threads work great for thrums. You simply tie a hank of
them to your bench, separate hanks for separate compounds. When you
need to clean a small area, grab a thread from a hank, rub it across
your compound (I use white diamond for burnishing and black rouge for
polishing), thread it through your piece, and thrum away. Eventually,
the thread will wear through and you’ll move to another one.
Weaving yarn comes in all sizes (gauges), including very fine. I
usually use cotton (unmercerized), but silk will also work. If you
don’t have a weaver’s guild nearby, or know a weaver, check your
craft store for cotton crochet thread (not yarn–it stretches). They
usually have it in white and bleached cotton, and it also works
really well. It’s strong and has a tight twist.
Get a piece of thread. Kite thread, butcher’s thread, embroidery
thread, household string, twine, whatever sort of thread you have
handy that’s about the right size to get into all the nooks and
crannies you’re looking to polish. Tie one end of it to something
solid and handy, pull it taught, and rub a bar of abrasive compound
on it. Viola, thrumming thread. Maybe do one in bobbing compound, one
in tripoli, and one in rouge, that way you’ve got a selection of
Beyond that, there’s a commercial product called Mitchell’s Abrasive
Polishing Cord. Comes in a bunch of different grits and sizes.
I use cotton thread designed for kite strings (several). Durable
under the heat & pressure generated while thrumming. It you need
something finer, then try cotton thread from the sewing department
(many & many threads.).
Jeni, Thrums can be made of any material that will fit into the areas
being sanded or polished but strong enough to withstand the thrumming
action and hold the sanding or polishing material. I commonly use
cotton string or a thin strand of leather (which I prefer). I’ve used
shoe laces, silk thread, sanding rope (available from places like micromark.com or even Harbor Freight). Small strips of plastic or
fish line can be used as well. Holding on the sanding or polishing
medium can be a problem but be innovative; rubber cement, olive
oil,…etc, make a slurry and see if it works. Copper wire laced
with diamond grit works quite well.
I have two pony-tails of thrumming threads hanging on the bench. One
pony-tail is charged with tripoli and the other with dialux white
(rouge). The threads are thick cotton about 0.7mm un-compressed and
one thread will get through a 1mm hole easily. I will use one thread
in a 1mm hole and a bunch of threads in bigger holes/cavities.
Charging is done by rubbing your brick of polishing compound up and
down the pony-tail until all threads are well charged.
Cotton threads don’t last very long before wearing thin and
breaking, but when charged with tripoli they can cut grooves if you
are not careful. Sweeping around rather than a sawing motion will
polish evenly without cutting grooves.
Bevelling the edges of sawn metal just enough to remove the sharp
edges will make a big difference in the life of the thread. The
edges of round holes can be given a twist with a ball or hartz burr,
and any hole can be de-burred with a graver or scraper.
I also have a few threads of 3mm parachord…some kind of braided
superplastic that works very well using the above methods for
polishing larger holes. Plastic threads will last longer but have a
greater propensity for cutting grooves instead of moulding into the
The short course, is any cotton fiber string and some form of
abrasive lapping type compound. That the string is coated in it can
be anything from a single thread to a larger dia packaging string
depending on the job. If you want a graduate course on the art and
zen of Thrumming I suggest getting a copy of “Form Emphasis for
Metalsmiths” by Heikki Seppa In addition to that it is a
gold mine of other info. Along with a health dose of humor. As he has
his tongue firmly planted, in his cheek!
Or you can locate a product called abrasive cord, like this at Lee
valley abrasive cord As it takes the mess out if the sizes will work.
I missed the beginning of this thread, so I am not sure what is the
need for thrumming.
Different areas require different approach. I never use commercial
thread of any kind. Thrumming usually is a next step after piercing.
A lot of time it can eliminated by piercing carefully and using an
old blade. If super-fine finish is required, I recommend 2 steps
Flatten copper wire, insert it into saw frame ( flexible frame works
better for this ) and use it with some tripoli and oil. Watch out, it
can cut as a saw.
Second step is a bit involved, but sometimes needs to be done. Double
the length of silk thread and wax it with beeswax very deliberately.
Find some old piece of fur coat and give it a haircut. Collect the
hairs and distribute small amount between waxed strands. Hair should
lie perpendicular to the strands. Some of it will fall, which is ok.
The ones that adhere is enough. Start twisting the stands of silk.
The twisting entraps the hair and that makes a very good thrumming
thread, which adapts to any shape of opening.
Do not expect good results right away. Thrumming is like burnishing
requires a lot of experience.
I’ve thrummed with everyday cotton string and find it quite useful.
I’ve also use dental flossing tape. Just about anything will work but
none of it lasts forever.
Regarding your sandpaper that breaks quickly, try adding some fiber
packing tape to the back of the sandpaper before you cut it to size.
I find it works quite well adding strength and also allows me to
mount a strip in my saw frame (not Lee’s (K)new saw frame).
Look for aircraft “lacing tape” basically it’s a very thin woven
tape made either from nylon or Teflon (nylon is stronger, but Teflon
wares less). Both kinds are available waxed or unwaxed. Waxed is
better for thrumming with grits as the wax will carry the grit. The
unwaxed are better for polishes as the polish is usually premixed
with wax. These tapes come in widths from 1/16" and in thicknesses
from 1/32. Down side is that you usually have to buy a whole bobbin
(250’ to 500’ depending on width/thickness of the tape), and the
stuff lasts a long time in service!
For crisp flat surfaces/corners I like to fit a bit into my saw
frame tighten it as much as I can and then go at it. Works like a