UNSECURED REVOLVING DEMAND PROMISSORY NOTE

Section 1 .    Promise to Pay .   For and in consideration of value received, the undersigned, Kronos Worldwide, Inc., a corporation duly organized under the laws of the state of Delaware (" Borrower "), promises to pay to the order of NL Industries, Inc., a corporation duly organized under the laws of the state of New Jersey (" NL "), or the holder hereof (as applicable, NL or such holder shall be referred to as the “ Noteholder ”), the principal sum of FORTY MILLION and NO/100ths United States Dollars ($40,000,000.00) or such lesser amount as shall equal the unpaid principal amount of the loan made by the Noteholder to Borrower together with interest on the unpaid principal balance from time to time pursuant to the terms of this Unsecured Revolving Demand Promissory Note, as it may be amended from time to time (this “ Note ”).  This Note shall be unsecured and will bear interest on the terms set forth in Section 6 below. Capitalized terms not otherwise defined shall have the meanings given to such terms in Section 16 of this Note

Section 2 .    Place of Payment .  All payments will be made at Noteholder’s address at Three Lincoln Centre, 5430 LBJ Freeway, Suite 1700, Dallas, Texas   75240-2697, Attention:  Treasurer, or such other place as the Noteholder may from time to time appoint in writing.

Section 3.   Payments .  The unpaid principal balance of this Note and any unpaid and accrued interest thereon shall be due and payable on the Final Payment Date.  Prior to the Final Payment Date, any unpaid and accrued interest on an unpaid principal balance shall be paid in arrears quarterly on the last day of each March, June, September and December, commencing December 31, 2008.  All payments on this Note shall be applied first to accrued and unpaid interest, next to accrued interest not yet payable and then to principal.  If any payment of principal or interest on this Note shall become due on a day that is not a Business Day, such payment shall be made on the next succeeding Business Day and the payment shall be the amount owed on the original payment date.

Section 4 .    Prepayments .  This Note may be prepaid in part or in full at any time without penalty.

Section 5 .    Borrowings .  Prior to the Final Payment Date, Noteholder expressly authorizes Borrower to borrow, repay and re-borrow principal under this Note in increments of $100,000 on a daily basis so long as:

Notwithstanding anything else in this Note, in no event will Noteholder be required to lend money to Borrower under this Note and loans under this Note shall be at the sole and absolute discretion of Noteholder.

Section 6 .    Interest .  The unpaid principal balance of this Note (exclusive of any past due principal) shall bear interest at the rate per annum of the Prime Rate less one and one half percent (1.50%).  In the event that principal or interest is not paid within five Business Days after such payment was due or declared due, all past due principal and past due interest owed under this Note will bear interest at rate per annum of the Prime Rate plus four percent (4.00%).  Accrued interest on the unpaid principal of this Note shall be computed on the basis of a 365- or 366-day year for actual days (including the first, but excluding the last day) elapsed, but in no event shall such computation result in an amount of accrued interest that would exceed accrued interest on the unpaid principal balance during the same period at the Maximum Rate. Notwithstanding anything to the contrary, this Note is expressly limited so that in no contingency or event whatsoever shall the amount paid or agreed to be paid to the Noteholder exceed the Maximum Rate.  If, from any circumstances whatsoever, the Noteholder shall ever receive as interest an amount that would exceed the Maximum Rate, such amount that would be excessive interest shall be applied to the reduction of the unpaid principal balance and not to the payment of interest, and if the principal amount of this Note is paid in full, any remaining excess shall be paid to Borrower, and in such event, the Noteholder shall not be subject to any penalties provided by any laws for contracting for, charging, taking, reserving or receiving interest in excess of the highest lawful rate permissible under applicable law.  All sums paid or agreed to be paid to Noteholder for the use, forbearance or detention of the indebtedness of the Borrower to Noteholder shall, to the extent permitted by applicable law, be amortized, prorated, allocated and spread throughout the full term of such indebtedness until payment in full of the principal (including the period of any renewal or extension thereof) so that the interest on account of such indebtedness shall not exceed the Maximum Rate.  If at any time the Contract Rate is limited to the Maximum Rate, any subsequent reductions in the Contract Rate shall not reduce the rate of interest on this Note bel