The blob brush in Illustrator CC CS6 etc can be found beneath the paintbrush tool or use shift+B to select the blob brush. The blob brush uses fills and not strokes. The blob brush has a number of settings such as size, how it is selected, fidelity etc. The Illustrator blob brush can be filled with all kinds of Illustrator colors. You can add strokes to the blob brush to add a border to the artwork. You can use the blob brushes with other paths and they can be blended into the blobs. It is a tool that is great for creating all kinds of amazing shapes. You can apply the blob brush in straight lines by holding down the shift key in Illustrator. You can add randomization to the blob tool. You can also use the blob brush as an excellent source for new symbols in Illustrator simply by dragging any created design into the panel. You can also add effects to the blob brush. The blob brushes can be used once or multiple times to create basic artworks as well as more complex brush strokes and artworks. This tutorial shows you how to start with the Illustrator blob brushes and the settings and how to apply via the Illustrator toolbar. It also shows a number of variations such as adding strokes and live effects to the powerful painting tool
Go to the paintbrush tool in Illustrator toolbar
Select the second tool 'blob brush'
Set the color of the fill
Double click the icon of the blob brush to change size etc
Apply blob brush to artboard
You can see the settings for the Illustrator's blob brush tool
double clicking the icon
there a number of settings such as keep selected, merge only, fidelity, size, angle and roundless. It has a similar look to the Photoshop brush tool with size and angle etc. The keep selected and merge only with selected are very useful if you want the blobs to stick together and create an extended path (though, you can also use the pathfinder to unite the results). The size and angle etc are great for creating slightly different brush strokes, more like the calligraphic brush strokes. There are also a few additional options such as having a fixed size or introduce randomization and variation for the size (as well as angle and roundness) as well as settings for an artpad / pen.
The Illustrator's blob brush can be filled with gradients as well as solid color and also patterns
You can add the Illustrator blob brush stroke in a straight line by holding down the shift key.
You can also see on the right, the blob brushes have been applied in a straight line by holding down the shift key. You can apply them
You can use it to create all kinds of characters as well such as a Z shape.
As you add the artwork, you will only see the fill being added but you can always add a stroke on completion as well as other effects such as live effects / blurs / additional fills etc via the appearance panel.
You can also then add width profiles to the blob brush.
Apply the blob brush
Go to the stroke settings and set color etc
Apply a width profile
Depending on the selection set for the blob brush tool, you can merge with other paths already created (circles etc)
select the Illustrator blob brush tool
double click to see the options to see that merge and selected are on
Apply brush strokes to path such as circle
You can control the merging by only merging with selected check set to on. You can also add the strokes and then add additional paths to that via the pathfinder combine / unite.
You can also use the subtract to add perhaps add spots and dots to the artwork. You can also add them to symbols (in editing mode) and can find a lot of different symbols on this site for use with the tool such as grid and tabular designs symbols for Illustrator and heart symbols and romantic shapes for Illustrator
One main issue with the tool (whether accurate or smooth), a lot of points can be created unless you add a very basic stroke. You can always use the various tools such as simply etc to remove some of them (personally the best tool is Astute Graphics' VectorScribe plugin)
Sadly, the randomization and variation is not with the blob brush single operation but only on re-applying the brush so if you apply one stroke with a variation set to 20pt (and size 10pt) you will get a 30pt or perhaps 15pt etc but not within the actual path itself.
The randomization actually works nicely with adding them as single spots (you don't have to add the tool as a long single stroke).
Go to the blob brush settings via the icon
set size to 90pt
set to random (to the right of the size)
Set the variation to 40pt etc, obviously you can set the size and variation to different values. You can also use other settings as well such as pressure. See the image on the left for a variation of dot blob brush sizes added in blue and then in orange, you have small blobs added and larger blobs and a lot of variation in between
It would be great if there was a randomization of color available as well but there is not though you always just change the color via the fill color in the toolbox as you add the artwork. You can also randomize the result by using the color guide tool.
You can use the Illustrator blob brush strokes to create other presets.
Simply add a blob brush
drag to the symbol panel
select item in the symbol panel
use with the sprayer tool.
You can also do the same with the swatches if you wish to create a tile and you can use the tool in the pattern editor. The result can still be added to using the same features of the tool to merge the fill. With the latest CC 2017 / 2015.1 release of AI, if you add the artwork as a symbol preset then you can also now add it as a dynamic or static item and if added as a dynamic then you can use the artwork as a master and add color and strokes etc to the instances added to the artboard.
The image on the right has been modified by the symbol spinner as well and you can modify the applied spray of the blobs in countless ways (as well as combining them with effects and styles etc)
Personally, not sure why the blob tool is not on the same toolbox as the erase tool as it is the same tool but inverted. The eraser tool can be added across the applied blob brush stroke and break the art into new individual paths which can then be added to by additional strokes.
Once you have added the blobs (and you can add them as actual spots or in one continious stroke) you can add effects such as tweak or roughen or offset or glow etc and you can then expand the appearance via the object menu.
Or add graphic styles such as on the right