I do think that spraying might be the easiest way to get close to this affect. To me, it looks like a dip method of some type was used. I'd have to post more pictures to show why. If it was a spray method they would have had to use a conical spray vs flat spray I think. But I'm no ceramics artist.
The glaze is so pretty I thought it may be a known and well used technique. However, it could be lost to time. I'm going to keep hunting and if I figure it out I'll let y'all know.
The brick arch under the hearth has settled. The plan is to reinforce it with framing and bracing. We were discussing about taking the bed down a half inch or so and installing a semi floating concrete board panel as a decoupling layer as well.
Thanks everyone for your input!