<PAGE>

                                                                   EXHIBIT 10.27
                               AMENDMENT OF LEASE

         This Amendment of Lease ("Amendment") is made as of this 1st day of
August, 1998, by and between GMT Corporation, a Minnesota corporation, whose
address is 245 East Sixth Street, Saint Paul, Minnesota 55101 ("Landlord") and
BMC Industries, Inc., a Minnesota corporation, whose address is 278 East Seventh
Street, Saint Paul, Minnesota 55101 ("Tenant").

                                    RECITALS:

         WHEREAS, Landlord and Tenant are parties to that certain Lease
Agreement originally between Control Data Corporation and Buckbee-Mears Company
dated November 20, 1978, as amended by various amendments and agreements
(collectively "Lease"); and

         WHEREAS, Landlord and Tenant desire to amend the Lease upon the terms
and conditions set forth below.

         NOW, THEREFORE, In consideration of the foregoing and other good and
value consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

         1.       TERM. The term of the Lease for the entire Demised Premises
                  (except for the "PS-3 Space" covered by the Amendment of Lease
                  dated September 25, 1997) is hereby extended for 5 years
                  through February 29, 2004. The parties agree that the PS-3
                  Space shall be governed by the Amendment of Lease dated
                  September 25, 1997, and any amendment thereto.

         2.       OPTION TO EXTEND. Provided Tenant is not in default under the
                  Lease, Tenant shall have two (2) additional, consecutive five
                  (5) year options to extend the term of the Lease for the
                  Demised Premises. In order to exercise said options, tenant
                  shall notify Landlord in writing of Tenant's intent to so
                  extend the term of the Lease at least one hundred eight (180)
                  days prior to the expiration of the then current term of the
                  Lease. For each option period there shall be an adjustment
                  ("Adjustment") in the Basic Rental and the Tenant's annual
                  share of "CAM Charges" as defined in Section 5 of the
                  Amendment of Lease dated April 6, 1994, as said Adjustment is
                  defined in Section 6 of said Amendment of Lease dated April 6,
                  1994; provided the "Base Price Index" shall be the Price Index
                  last published prior to the end of the term then in effect.

         3.       RENT. Basic Rental and Tenant's share of CAM Charges shall be
                  as follows:
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<TABLE>
<CAPTION>
         SPACE             SQ. FT.       ANNUAL RENT/SQ. FT.        ANNUAL CAM/SQ. FT.
         -----             -------       -------------------        ------------------
         <S>               <C>           <C>                        <C>
         PS-B               17,377            $2.22                      $1.68
         FB                  9,640             2.83                       1.68
         R-5                29,115             3.88                        .31
         R-6                29,115             3.88                        .31
         PS-1                7,170             3.88                       1.68
         PS-2                2,664             3.88                       1.68
         S-228               1,782             3.88                       1.68
         S-500               8,752             3.88                       1.68
         PS-5B               1,078             2.22                       1.68
         PS-6                3,013             3.88                       1.68
         PS-601              2,586             3.88                       1.68
</TABLE>

         4.       Tenant shall have the right, with a 150-day notice to
                  Landlord, to reduce the Demised premises in the Park Square
                  Building as follows: on the 5th floor, by any or all of the
                  9,830 square feet; on the 6th floor, by any or all of the
                  5,599 square feet; and on the 2nd floor, by any or all of the
                  4,446 square feet. The reductions must occur in different
                  calendar years, unless Landlord has already released the
                  previously reduced premises. Each notice to reduce shall cover
                  premises only on a single floor.

         5.       Tenant shall have the right to lease additional space in the
                  Building, if available, at the current rate Tenant is paying
                  for similar space.

         6.       Except as specifically provided herein, the terms and
                  conditions of the Lease shall continue in full force and
                  effect. In the event of any inconsistency between the terms of
                  this Amendment and any other terms of the Lease, the
                  provisions of this Amendment shall control.

         IN WITNESS WHEREOF, This Amendment has been executed as of the date set
forth above.


LANDLORD:  GMT CORPORATION                      TENANT: BMC INDUSTRIES, INC.

By:  /s/ Henry Zaidan                           By:  /s/Benjamin A. Teno
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Its:  President                                 Its: VP/GM
    ---------------------------                     ---------------------------