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Tessellated Mosaic Workshop


                           Most of these photos are from the 2011 and 2012 sessions.


Special thanks go out to:


- Jason Detert

- Carrie Mathison

- NRB Metals, St. Charles, MN

- The Staff and Students at Fillmore Central High School
















Local Artist doing what he loves, Fillmore County Journal, Sep. 30, 2011


Fillmore Central art students visit foundry, Fillmore County Journal, Jun. 5, 2009



This ongoing project for Fillmore Central High School in Harmony, Minnesota dates back to 2009. To kick it off, Artist Karl Unnasch designed and constructed a tessellated (set mosaic) pattern; within this pattern, each student has had the opportunity to create a cast iron tile bearing their own unique design.


The project not only teaches students about mold-making and metal-casting processes through first-hand experience, but becomes a permanent and very personalized public artwork on the walls of their school.



The project began in 2009 and continues to grow and evolve.

Karl and the Art Class Instructors install the finished work during off-hours with the help of student volunteers.

Students scratch designs/patterns/imagery into one surface of each sand core. 

The cores are inserted into master molds providing the surface pattern for the tiles. 

Once molten iron is poured into the molds, the resulting castings retain a reverse relief pattern of the crafted designs/patterns that the students carved into each core. 

Once cooled, the castings are removed from the molds, excess metal (called ‘returns’) is cut/ground off, the tiles are shot-blasted, and mounting holes are drilled into each. 

The semi-finished castings are returned to the art class for re-distribution to their respective students. Stove black is applied by the students to the surface of the metal as one would apply shoe polish. The excess polish is rubbed off and the plates are allowed to set and dry for 24 hours.

Seal coating is applied to preserve the patina created by the students. The tiles are allowed to set and dry for 24 hours once again. 

The finished tiles are installed with concrete fasteners on a stairwell wall next to the auditorium in the students’ school. 

Karl designed and constructed a set of multiple piece core patterns for the original overall layout. Each year, he produces sand cores from these patterns for the mold-making process and delivers them to the Art classes. Individual sand cores are distributed to each participating student. Under Karl’s instruction, students then scratch designs/patterns of their own invention into each core. 

The cores are then delivered by Karl to the NRB Metals foundry, where he makes receiving molds into which the cores will be inserted. 

Each tile is a casting of the artwork of each student who takes part in the project.


Most students choose to design a graphically rendered text for their tile.

Some years, students take a field trip to the foundry to  witness the process first-hand — from a safe distance. 


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Project Page

Tessellated Mosaic


An Expanding Iron Tile Mosaic

Created via a Series of Workshops

by Karl Unnasch,

for and with Fillmore Central High School

Students and Staff,

in Harmony, Minnesota


An ongoing project since 2009

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Pilot Mound Design.

Harmony, Minnesota



A Growing Legacy


created by Public Artist Karl Unnasch

in collaboration with

Fillmore Central High School

Staff and Students



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Tessellated Mosaic

Sometimes, a field trip to Karl’s studio in Pilot Mound is a part of the project — such as here in 2015.                    (Photo credit: Michael Cimino)

“[...] a great project for all the students; they have the opportunity to leave a piece of themselves behind.”



Fillmore County Journal, 2009