Late 19th century equine painting with Irish wolfhound

Terrible condition. Paint was powdery and flaking, the canvas torn, and the plaster frame had moulding missing, was covered in a tar grease with embedded soot and pet hair.

The paint's binder had collapsed and rubbing the image resulted in pigment stain crumbling away. The whole canvas was covered in tiny blisters where the paint was detaching from the support.
A challenge! How to clean it the painting without removing the image or permanently embedding  the grime.

The finished painting - without varnish.