Tuesday, January 2, 2018

Burning bowls

While I love the effect of milk paint, especially the way layered colors gain character through use, I have been experimenting recently with shou sugi ban.  Shou sugi ban (焼き杉), literally "burnt cedar board" or "grilled cedar," is an ancient Japanese technique of preserving wood by charring.  The burnt surface is dark, rich and textured,  especially after oiled.  It is also bug, fire and water resistant, allowing some structures to last for hundreds of years.  You can get lots of different effects with different burn times and treatments.
https://goo.gl/fepi8s
When used on bowls, this technique can create some really striking effects.  The surface is velvety smooth and inviting to the touch.  Visually, the matte black sections seem to suck in all light, such that if you char only the bottom of the bowl, it makes the upper rim appear to float in space...




The process is pretty easy, and there are lots of videos online to get you started--just burn, brush, wash and oil.  As nearly all of the tutorials online focus on burning cedar siding, I thought I would share some insights into how this technique might translate to smaller birch bowls. 

As I understand it (and I am no chemist!), charring wood alters the surface of the remaining material.  The cell walls of wood are made up primarily of cellulose, which is hydrophilic and helps draw water through the tree.  Lignin takes up much of the space within the cell walls and helps give strength to the plant.  Lignin is hard and hydrophobic.  When you burn wood, the cellulose vaporizes first as it burns at a relatively low temperature, leaving behind lignin, which burns at a higher temperature.  Thus, charring creates a hard, hydrophobic skin of lignin and carbon on the wooden bowl.  While I don't care about the other benefits of shou sugi ban (termite and fire resistance, for example), I sure like the idea of my bowls resisting wear and water!

Most videos online show people using a roofing torch on cedar planks, but that is overkill for a little bowl. I use a simple Bernzomatic propane torch, which costs about $30.


Obviously, it is preferable to work outside on a non-combustible surface.  If you are going to burn the outside of the bowl, I recommend propping it on top of an empty tin can.  No matter how dry your bowl is, as you burn the outside moisture will be driven from the inside, and it needs a place to go.  Be prepared for the bowl to warp a bit, even if it is "dry."  I have not had one crack yet, but you can see it change shape through the process. I try to keep the flame moving over the whole bowl for a bit, bringing the entire piece up to temperature before really working on one spot.  

Heat bounces.  As you approach a foot, bead or decorative cut, you will find that the heat does not make it into the valley of the cut.  Instead, it will project out and burn the surface at a right angle.  This means you can cook the foot pretty good trying to get heat into the valley between the bowl and the foot. I have learned to embrace these lighter areas.


Here you can see the light line around the base of the foot, yet heavy burning on the rim of the foot itself.  Heat bounces and does not penetrate into valleys very well. Embrace it.
The other reality that comes from this bouncing effect is that a bead can be used as a "wall" to separate a burned section from a non-burned section.  
Here the bead acted as a "wall" and helped protect the rim band from burning and proving a sharp transition.
Inscribe first, and then kiss the surface with the torch for a nice contrast.
I can also envision how one might add a design by using masks to protect some areas from burning.

If you do burn right up the the rim, be careful of thin lips.  They will catch fire faster than the rest of the bowl, and if an ember forms it can burn a notch in the lip pretty quickly.
Here you can see both a decorative cut spared from burning, which is a nice bright line, and a rim burned too much, where an ember formed and burned down into the bowl.
Once the burning is done and the bowl is cool, move on to brushing.  I recommend a nylon brush to remove the excess carbon.  If you don't remove the excess carbon now, the bowl will leave marks on surfaces later.  Just like when you sand milk paint, watch out that excess soot does not stain the rest of the bowl.  I am often surprised by how much of the luscious black comes off with brushing.  Don't worry, once oiled that black color will come right back.  


Here the bottom half of the bowl has been brushed with a nylon brush. The top has not.  No worries--that brown post-brushing color will turn black with oiling.    
The reason I like the nylon brush over a rag is that rags often leave behind fibers, especially if you rub against the grain.




I then recommend rinsing the bowl, again being careful not to let the loose soot stain other parts of the bowl. Some people blow the dust away with an air compressor.

Once dry, oiling is pretty straight forward, though be careful not to rub excess oil from the dark areas onto the lighter areas.  Here you can see the oiled wood returning to a nice, dark shade.


Here the top half has not been oiled yet, but the bottom has.  Nice, luscious black tone.   
After oiling.
I am now experimenting with chip carving burnt bowls.  The charring is not just a patina, it goes down a ways, so only the bottom of a chip reveals the unburnt wood.  But I like the effect.  I was always hesitant to chip carve painted surfaces, as the pigments dull the knife edge.  With shou sugi ban there is no such concern.




So, there you go. Hope that helps.  Enjoy and be safe.


 焼き樺椀

  "burnt cedar bowl"



Friday, December 22, 2017

Platform project

A few years ago I built a play structure for the girls, which they dubbed the "pirate platform:" zipline onto the platform, slackline, hammock, etc... 
Lovely place to take your morning coffee.

Recently, my youngest daughter Mae asked that I build another, maybe with the possibility of adding a treehouse at some point.  We will see...
Main beams hoisted and bolted into position.  I was super thankful for my brother's help on this part of the job.  Each beam was super heavy, made of two 2 x 12 x 14' pressure treated (and wet!) boards.  Did not have a block and tackle, so it definitely took two people to get them into place.  Thanks bro!

 Joists now span the gap between the beams.  One challenge I had was after the end caps went on, how to adjust the position of the platform on the beams.  I laid boards out where I thought they should go, but on second look the whole platform hanging over one side more than I liked.  How to slide everything over?

Answer? Counterweight.  That board dangling just off the ground is tied to lines that run up through pulleys and then down to the joists.  This relieved just enough weight for me to push the platform around on the beams and center it.
 How to add the endcaps when I am the only one on the job?  Answer: use joist hangers upside down, which now guide the cap onto the joists, ensure the joists are equally spaced, and keeps the cap from falling to the ground.  Made sense to me at least...

 Not easy to screw those caps into place.  Climbing gear made the job easier, and fun.

 The client came by for a peak at the progress.  She seemed quite happy.  Love the overalls!

 Joists, end caps and blocking is done.  Feels pretty firm.  Time to start decking.

Final result.  Enough room to hold a party, though I gotta get railings and a staircase up before we do that.  But it has a nice view of "Blueberry Hill" across the way.
This was another big project, building a gravel patio on top of this hill.  Four yards of 3/4" gravel up there.  Had to rent a small tractor for that job...

Finished just in time for "Jug Band" Camp.  Here a few of us are sitting out on top of Blueberry Hill, on the new gravel patio, making noise.  You can see a six-person tent on the platform in the distance.

New shop

Settling into a new shop space, and it makes me happy. 

For the past thirteen years we have lived "on campus" at the school where I work. I am very thankful for that time in our lives, especially as it let us save money for a getaway in New Hampshire.  My first shop was set up there, which meant most of my woodworking happened during vacations.  But this spring we finally moved off campus and into our own home (just a few miles down the road from my job.) 



It is a great little house for a lot of reasons, but I was especially excited about the possibilities for a basement workshop. 

You can see it has a fireplace, which took a bit of cleaning before it would function.  The chimney sweep said it had not been cleaned for years... 


But once I got things sorted, it is now feeling homey, especially when I have the fire going.


I am still sorting out the lighting situation, and I need to paint and get tool racks up.  But this is a good start.  Makes me happy.



Monday, December 11, 2017

Mbiras/Kalimbas

Winter affords the carver a range of pleasures: the joy of carving by the fire on a long winter night, giving away craft during the holidays, and scoring that new tool.  But it also comes with challenges.  In the northeastern U.S., winter means substantially drier air in the workshop.  Drying times suddenly shorten, and what once took days or even weeks to settle into its final shape now snaps to form in a matter of hours.  For the bowl turner this means treating all but the thinnest work very carefully, wrapping it up in cloth or paper bags, burying it in shavings, etc...   Add to this the fact that some of us lucky souls have a wood stove or fireplace in our workshop.  I moved into a new home recently, and my new shop has a working fireplace.  I can not tell you how awesome this is.  Just sweep the shavings into the fireplace, toss a match, and viola--a clean and warm shop.  But this wonderful feature is not so wonderful when you find a batch of bowls ruined by overly hot and dry air.

If this has happened to you, and you don't know what to do with the bowls with the checked rims, you might try building a "mbira."

These African instruments are pretty easy to make.  Flatten the rim of the bowl (which lets you carve out the cracked lip where the rings were tight).  Plane a thin top (I used pine here, but I am told that the material used for the top of an instrument has a big impact on the sound quality.  Koa? Spruce? Mahogany?)  Glue a block of wood to the underside of the top and put t nuts into the block, into which you can anchor the screws that hold the aluminum rod above.  Glue the top onto the bowl, trim to shape, and bore a sound hole.  The silver bar is aluminum (easy to machine), smaller bar is brass (looks nice and matches the brass screws), and the tines are made from a sewer rod (a new one!)  You tune the instrument by pushing the tines in and out to get the right tones.  Lots of different tunings--I tuned mine to the C-scale, diatonic--good for jingle bells.







Tuesday, January 24, 2017

I need to make a reamer and tenon cutter

I am writing this as a reminder to myself: I have wanted to make stronger legs for benches and stools, and I now realize that I need to make a reamer (and an accompanying tenon cutter).  Dave Fisher's recent post got me started on this.
Here is an article from greenwoodworking.com

Here is an article from Tim Manney on making a matching tenon cutter.

Eric, do this!

Monday, January 23, 2017

Spoon "tattooing"

Been on a kolrosing kick these days.


Kolrosing is a scandinavian technique whereby the carver makes shallow cuts into the surface of the wood and drives a pigment into the cuts.  It is similar to scrimshaw designs in ivory and even tattooing in skin.  While the wood does not "heal" as a tattoo would, the fibers can be burnished to lay over the cut, and once a drying oil like flaxseed is applied and dries, the pigment is pretty well held in place.
There are lots of great resources on the web to get you started.  Del Stubbs at Pinewood Forge has a great intro to kolrosing page and sells really nice kolrosing knives, though you can use most any knife.  His are nice because the blade has a sweeping radius, which allows for tight turns without the blade "jumping" out of the piece, and the angle of the blade lets the edge enter gradually, compressing/cutting the fibers neatly even if you are cutting against the grain.  I also like the width of the blade, which forces the wood fibers apart and creates a good pocket for the pigment. Finally, the round handle reminds me of a pencil, and as such can be spun to achieve tight turns (if you are careful!)
No need for deep cuts!  They will be marginally darker and wider than shallow cuts, but only barely, and if you really auger down into the wood you will have a hard time making smooth lines.  Watch the grain direction as your lines come together.  You can inadvertently dislodge a chip under certain circumstances (see the stem of the leaf on the right in the image below.)  Use really fine powder.  Well ground coffee works great, but I like taking the powder that remains at the bottom of the grinder.  Powdered coffee like Nescafe works well too.  I have also experimented with milk paint powder for a colored effect, though the tone is hard to distinguish.  You don't necessarily have to sand the wood surface before hand, but treating the wood with a rub of beeswax or another sealant can keep the coffee from staining the surrounding wood and hiding your design.  Lots of people like basketweave designs, but I prefer more freehand and flowing lines.  It is challenging to get fluid curves.  Sometimes it works out, like here:

Other times it does not...
The stamen got a bit mauled.  That is a really tight curve.  You can also see how small lines, cross hatching, even stippling can give volume and detail to the piece.  The lines are really narrow, so use lots of them.


Here, in an earlier post on some of my work, the spoon third from the left has some cross hatching to indicate shadow.  The one on the right was done with green milk paint.  It also lost some of its coloration, as I did not burnish the surface enough.  You can also sand the surface lightly to close the fibers.

I find that the hardest part of kolrosing is letting go.  After finishing a spoon that you feel proud of, it can be hard to take a risk and scratch it all up.  Like getting your first tattoo, or your first "visible" tattoo, it can be hard to get your head around permanently altering a pristine surface.  But once you cross that threshold, it can be hard to stop!

PS
After my pal Oliver came to stay for week, we traded spoons.  He chose one of my more heavily kolrosed spoons to take with him, saying something like, "Well, I have to take that one, because it is rad!"  His comment got me thinking.  What is "radical" about that spoon?

Is it the spoon's design?  Probably not.  There is nothing extraordinary about this spoon.  It is a nice spoon, but the design is not out of the ordinary.  Even some of the more particular elements of this spoon, like the asymmetrical bowl or the tiny finial, are in fact inspired by Oliver's spoons.  He would not find them radical.  Was the floral design itself radical?  Not so much.  Flowers, especially made up ones like this, are not "radical."  So what was "rad" about this spoon?  I think Oliver's response to the spoon is akin to the response many of us have to tattoos.  When we meet a tattooed person, we seldom explore the subject of the tattoos, or admire linework, shading or coloring.  Instead, one of the first and most prominent feelings many have is that the commitment of the tattoo, the commitment to permanently alter a pristine surface, is in itself radical, regardless of the subject or execution.  Kolrosing is rad, in itself.