Given an algebra $\mbfM$ we may adjoin an isolated zero to form an algebra $\infM$ satisfying all identities $u \approx v$ true in $\mbfM$ for which $u$ and $v$ contain the same variables. Drawing on the structure theory of P\l onka sums, we show that if $\mbfM$ is a finite, dualisable algebra which is strongly irregular, then $\infM$ is also dualisable. Turning the construction of $\infM$ upside-down for the two-element left-zero band, we exhibit a duality for quasi-regular left-normal bands.