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I intend draw a dark line 50mm / 2" large using a blowtorch on a piece of pine wood, but how to have a nice & clean line border ?

I thought of using sacrificial wood pieces or aluminium sheets as flame barrier but honestly I've no idea where to start.

I don't need the line to be black but just darker.

I've seen a "hot sand" trick but it's effective for edges only.

I'm targeting a rustic style, but I've no metal bars big enough to heat.

  • I though about sacrificial wood pieces but since you are going to burn them you would be changing their shape which would not be ideal. – Matt Apr 16 '15 at 15:01
  • Does it have to be a blow torch? You title is not explicit. Would you entertain other ideas like a stain solution? How big is your wood piece? A baking sheet would be a good choice for a solid line if the wood is longer – Matt Apr 16 '15 at 15:02
  • @Matt My piece of wood is approx 2m long 1m large. I will protect the finished piece with stain. What is a stain solution ? different stains with stencil masks ? – Nelstaar Apr 16 '15 at 15:13
  • @Nelstaar asking how to stain part of a piece would be a good, separate, question. You should ask it! – lars Apr 16 '15 at 17:47
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    I too am wondering if a blowtorch is the most appropriate tool to use. I realize that it is a large piece, but do not know how large an area needs to be marked. Wouldn't a wood burner from a hobby store or even a soldering iron work? – Michael Apr 16 '15 at 19:02
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bowlturner's answer is correct, and will probably give you the results you are looking for. But it inspired me to experiment, mostly to see how sharp an edge I could get.

Hardwood Guide

wood burning with hardwood guide

As you can see, just setting down a piece of hardwood makes an obvious, if not sharp, line. The main problem is getting into the corner. I tried to only scorch the pine, so I couldn't wait for the flame to burn the inside edge.

Metal Guide

wood burning with metal guide

This time I slowed down and concentrated on getting the flame into the corner. I also used a steel guide, but I didn't see a difference from the hardwood guide.

As you can see, this one is quite well done (burnt), but it does have a sharper edge.

Masking Tape

wood burning with masking tape guide

Not great, but not as bad as I thought. The heat melts off the adhesive and it's easy to burn through the tape a little bit, but it made an okay line. I cleaned off the adhesive with mineral spirits.

Routed Recess

wood burning with routed recess

I also tried routing out a shallow area to receive the burning, with the intention of planing off the high spot. This didn't work though, because it creates another inside edge that the flame can't reach. But if you could somehow get the burned part right up next to a freshly-planed edge, I'm confident that this would give you the cleanest, sharpest edge possible.

Source for all images: me

  • Impressive experiments, I'll try the hardwood mask solution with edge renewal each time. – Nelstaar Apr 17 '15 at 9:01
  • If you're going to plane it anyway, you could route just the tiniest bit past where you're wanting the line. Then the corners wouldn't matter as much. I'd be interested to see what that routed out board looks like once you've planed it. – Charlie Kilian Apr 29 '15 at 20:40
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I am assuming you are using the torch to 'scorch' the wood and not really burn it. I think that clamping another piece of wood as a "sacrificial piece" onto the line should work just fine. Doing this light enough and you can reuse the one board over and over again. if it is getting to burnt than run it through the jointer to square it up again.

Using a hardwood for the boarder piece it will last longer and hold up better, but another piece of pine can work too. a piece of metal might need to be thicker to work as well so that it doesn't transfer the heat to the wood giving you a wavy line under it.

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If you only need to present a darker wood, but not charred or completely black, aluminum foil or aluminum tape should work well.

Aluminum is great because it conducts heat very well, spreading the heat harmlessly across a larger surface of metal. wide aluminum tape should give you a very sharp line without the problems that the corners of higher templates present as described in lars' experiments.

If you are careful, masking and other tapes may work as well - the heat goes towards burning the tape and not the wood, protecting the wood underneath.

  • I'am afraid that the glue from the tape change the wood. – Nelstaar Apr 17 '15 at 8:58

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