Teaching about the "bone effect"

I know many of you conduct workshops/classes on type.
I'm trying to find a good way of teaching the concept of bone effect and why it's important to smooth out the joining of rounded and straight segments.
Can you please share your experience and whatever worked best for you in explaining this particular point?


  • I never heard of that term. It sounds pornographic.
  • The term is mentioned and illustrated here: I think it's one of the harder illusions to see. I haven't taught type design, but I would think the only way to get it across is to do some characters right and wrong, and show the difference, in context.
  • John HudsonJohn Hudson Posts: 1,774
    edited July 2013
    Yes, it's an optical illusion, so it needs to be demonstrated, not explained. By the way, it is more pronounced when the straight segments are vertical than when they are horizontal.
  • You already showed us how to teach the concept in that webpage!
  • Paul van der LaanPaul van der Laan Posts: 206
    edited July 2013
    Yanone’s Speed Punk is a great tool that can visualise this effect. On his website he makes a comparison between bezier curves, and how rollercoasters are constructed in real life:

    “Taking off in a roller coaster from the flat into a perfect circle loop would brake your spine, as the curvature would infinitely increase from the straight line to a fixed amount of curve speed in the circle. Or imagine the impossibility of your car's steering wheel needing to be turned instantly by a fixed angle from the straight road into a curve. Instead, any moving object turns into a curve progressively, starting with no curvature and slowly increasing it over time.”
  • Nick ShinnNick Shinn Posts: 1,478
    It's related to the concept of "level/vertical".
    We are able to distinguish very slight variances -- less than one degree -- from true level or true vertical, but not between, say 47˚ from 48˚.
    IMO this relates to the way we process information categorically, with the concept of “true” being markedly different from even the slightest deviation.
    This is why a transitional buffer zone is required between straight and curve, because we pay particular (and distracting) attention to the transitional point at which the line changes from one category—dead straight—to another.
  • James MontalbanoJames Montalbano Posts: 934
    edited July 2013
    Never heard of that term, but Ed Benguiat taught me how to correct that 30 years ago. Before there were digital outlines.
  • James, did he provide you any explanation while teaching you how to correct it?
  • Ed's point was to soften the transition from the curve to the straight. Mind you this was in the days of ruling pens and compasses. The trick was to scribe the arc with the compass and have it fall short of having it meet the straight, by a millimeter or so, then touch up the connection to minimize the abrupt transition of straight to round. It usually required a bit of white paint. With a digital outline I tend to move the tangent point back into the straight and let the curve take its time as it emerges. Another approach I use is to not ever have a true straight and have the arc of the curve enter what looks like a straight segment but is really a very long almost flat curve. I like this approach a lot!
  • Another approach I use is to not ever have a true straight and have the arc of the curve enter what looks like a straight segment but is really a very long almost flat curve. I like this approach a lot!
    This “no true straight line” idea is indeed interesting. I’ve been thinking about avoiding dead straight lines too. Do straight lines ever happen in “real world”? I mean, outside digital calculations and digital printing.
  • Chris LozosChris Lozos Posts: 1,206
    Even the horizon line is not truly straight, it follows the curvature of the earth. A straight line is a vector or an easily described path.
  • Crystalline structures get pretty close to straight. Plumb-bobs and lasers too.
  • Bob Newhart was straight.
  • Chris LozosChris Lozos Posts: 1,206
    Yes, but he had to deal with "Other Brother Darrell"
  • I believe this is what engineers and mathematicians refer to as "clothoid curves" and "clothoid transitions." Some years ago there was a profile piece in The New Yorker about a German guy who was one of the world's leading designers of roller coasters. He talked quite a bit about these curves, and how they avoid breaking people's neck on roller coasters, and how they're also used in designing off-ramps on highways and high-rise parking lot ramps. With the right clothoid curve, you can keep your steering wheel in one position all the way to the top floor of the lot. I heard of a guy (probably from Berlow) who broke his neck on the Martha's Vineyard ferry reading a sans serif lowercase r. He'd be alive today if clothoid curves had been used.
  • Dave CrosslandDave Crossland Posts: 1,051
    See http://levien.com/phd/phd.html on clothoid curves :)
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