[Fizzlemizz]

Used in the artifact power button template:

<Layer level="OVERLAY" textureSubLevel="2">
	<Texture parentKey="Icon">
		<Anchors>
			<Anchor point="CENTER"/>
		</Anchors>
	</Texture>
</Layer>
<Layer level="OVERLAY" textureSubLevel="1">
	<Texture parentKey="IconDesaturated" desaturated="true">
		<Anchors>
			<Anchor point="TOPLEFT" relativeKey="$parent.Icon" />
			<Anchor point="BOTTOMRIGHT" relativeKey="$parent.Icon" />
		</Anchors>
	</Texture>
	<MaskTexture parentKey="CircleMask" file="Interface\CharacterFrame\TempPortraitAlphaMask" hWrapMode="CLAMPTOBLACKADDITIVE" vWrapMode="CLAMPTOBLACKADDITIVE">
		<Anchors>
			<Anchor point="CENTER"/>
		</Anchors>
		<MaskedTextures>
			<MaskedTexture childKey="Icon"/>
			<MaskedTexture childKey="IconDesaturated"/>
		</MaskedTextures>
	</MaskTexture>
</Layer>

The MaskTexture childKeys point to the two textures created.
The file TempPortraitAlphaMask is just a white circle on transparent background presumably used for creating an overlay mask. I don't use the default artifact power bar so garner from that what you will.