Ionic Ion-Button icon-only

For Ionic 4 - <ion-button fill="clear">

You can use the fill property now, e.g:

<ion-button (click)="onClick()" fill="clear">
      <ion-icon slot="icon-only" name="home"></ion-icon>
</ion-button>

Adding a clear attribute should give the result you want if i understand correctly:

<ion-content class="bg-image" padding>
</ion-content>
<ion-footer>
  <ion-toolbar>
    <button ion-button icon-only clear>
      <ion-icon name="home"></ion-icon>
    </button>
    <button ion-button icon-only clear>
      <ion-icon name="add"></ion-icon>
    </button>
  </ion-toolbar>
</ion-footer>