Thank you Rod.

Ok here is the Wallace brush (sized at 75 -spaced at 144) on a transparent layer.
I created the one layer by making (painting with the brush) a sort of spiral from the outside in. DONT overlap any letters.
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Now Filters>Map>Map Object. Map to sphere - new image - transparent bg.
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You get something like this -
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now it's cleanup time. Remove all outside globe imperfections, partial letters, blurs ect..ect.
Until you have something like this image.
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Now just duplicate the layer two more times and rotate each layer so their all different.
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You could also use Filters>Enhance>Unsharp mask before duping. It may be sharper that way.

If you need to fill the center and other areas like i did, just use the brush on 3 new transparent layers at the sizes you need.
Place each new brush size layer above the corresponding distance ratio (xcf included so you understand that better).
And volia! You have a pretty decent looking letter/number globular cluster.

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This was a quicky. With first brush computations you may be able to get a starting globe with NO imperfections and no blurs! I am sure this can be done in GIMP now with just GIMP tools and of course Wallace's brush. Thanks Wallace!.

Have fun with it.
XCF workspace file-

I was wondering if that glassy effect applied could be useful to Dinasset's idea to get a stained glass on the tiles.

Thank you Rod for your quick answer. I meant the look you got to the lettering ball with curves and filters. It's quite similar to the glassy letters. Could it be applied to little panels on a stained glass?, please take a look at "open challenge" if you can. I know that you get what it seems impossible, hehehe. Thank you so much.