Unicode character (hexagon) not displayed on some computers

Question

I have a huge problem. I just updated my websites homepage to display a unicode hexagon character: ⬢ ⬢ aka U+2B22
I made it 200px big and filled it with text. It looks good and works fine on my computer. With both Internet Explorer (win8) and Firefox 28.
I tested it on 5 different computers and it didn't work there! Tested with Firefox 28 and Internet Explorer (win7) on each device and on one computer even with the newest Chrome.

So what am I doing wrong? How is it possible that it works on my FF 28 and on 5 different devices with FF 28 it doesn't?

I already tried:

<?php header('Content-Type: text/html; charset=utf-8'); ?>  

and in HTML directly:

meta http-equiv="content-type" content="text/html; charset=utf-8" 

Is U+2B22 not part of utf-8?

Try it yourself here, scroll to the very bottom of: http://jtauber.github.io/articles/css-hexagon.html
For my PC it looks like this: http://250kb.de/u/140401/j/RzN1lYTL8fLJ.jpg
On other devices it looks like this: http://250kb.de/u/140401/p/VEeerGhyv4lM.png

I appreciate any help!

Answer 1

The character U+2B22 BLACK HEXAGON is included in a few fonts only. None of those font comes with Windows or with other widely used software, so in most computers, there is no font containing it. Moreover, browsers may fail to render the character even if some font in the system has it. For some more general explanations, see my Guide to using special characters in HTML.

In this case, the font setting is font-family: "Helvetica Neue", Arial, Helvetica. None of those fonts contains the character, so each browser tries to use other fonts in the system, in a browser-dependent order. In your own computer, you have a font that contains the character. You may have downloaded and installed it, or it may have come along with some software

What you could do is, alternatively,

a) specify, in a font-family declaration, a list of fonts known to contain the character. This could help against problems of browsers not finding a font, but this would not matter much.

b) use a downloadable font (web font, via @font-face). This would mostly be overkill if you just want one character for essentially non-text use. Fonts that contain U+2B22 are generally large.

c) use an image instead, possibly as a background image. This would be here the rational choice, especially since you would not use U+2B22 as a character in text but as a background of a kind.

Regarding the question “Is U+2B22 not part of utf-8?”, characters aren’t really part of utf-8. Instead, utf-8 is a transfer encoding for characters, and all Unicode characters (and, moreover, all Unicode code points) have representations in utf−8. Besides, the page mentioned does not contain U+2B22 as such but as the character reference ⬢, and this works independently of character encodings. Thus, this is not an encoding problem, but a font issue.

Answer 2

These computers on which it does not work do not have a font installed which contains a glyph for this particular character. That is all.

Solutions would include to not depend on users having fonts with such unusual characters installed and provide them as web font instead (which you might have to create) or to use an image, SVG or canvas instead.